Showing papers in "Mutation Research in 1968"
TL;DR: 96 mutants of yeast have been isolated which were more sensitive than wild-type to ultraviolet irradiation, and genetic analysis showed that many are inherited as single mendelian recessive mutations, and that they occupy at lest 22 different loci.
Abstract: 96 mutants of yeast have been isolated which were more sensitive than wild-type to ultraviolet irradiation. Genetic analysis showed that many are inherited as single mendelian recessive mutations, and that they occupy at lest 22 different loci. Survival curves show that in all the mutants the low UV-dose shoulder characteristic of the survival curve of wild-type yeast is absent or very reduced, but that the slopes vary from one mutant to the next and are often complex. 5 mutants are also more sensitive to ionising radiation than wild-type and 5 reduce the ability of yeast to sporulate.
282 citations
TL;DR: Results are in good agreement with the expected effect of the chemicals based on work with microorganisms and in an equimolar dosage, MMS is about 4 times more effective than EMS in inducing dominant lethal mutations in these cell stages.
Abstract: Methyl methanesulfonate (MMS) and ethyl methanesulfonate (EMS) induced a high frequency of dominant lethal mutations in mouse spermatozoa of vas and epididymis, testicular sperm, and late spermatids, and a low frequency in early spermatids. In an equimolar dosage, MMS is about 4 times more effective than EMS in inducing dominant lethal mutations in these cell stages. Neither N -methyl- N ′-nitro- N -nitrosoguanidine (MNNG) nor 2-methoxy-6-chloro-9-[3-ethyl-2-chloroethyl)amino propylamino]acridine dihydrochloride (ICR-170) induced dominant lethal mutations in spermatozoa of vas and epididymis, testicular sperm, or spermatids. These results are in good agreement with the expected effect of the chemicals based on work with microorganisms.
204 citations
TL;DR: Evidence is presented which support the concept that F 1male sterility, like F 1 male semi-sterility, has a basis of chromosome breakage, and the same dose of the chemical induced high frequencies of translocations among the F 1 offspring.
Abstract: Ethyl methanesulfonate (EMS) induced high frequencies of dominant lethal mutations in mouse epididymal spermatozoa and late spermatids and lower frequencies in vas deferens spermatozoa and early spermatids. Pre-meiotic germ cell stages were relatively resistent to the induction of dominant lethals and cell killing. The same dose of the chemical also induced high frequencies of translocations among the F1 offspring, the frequencies being highest among offspring from the germ cell stages most sensitive to the induction of dominant lethals. Evidence is presented which support the concept that F1 male sterility, like F1 male semi-sterility, has a basis of chromosome breakage.
115 citations
TL;DR: The effect of dose-rate on the induction of reciprocal translocations in mouse A type spematogonia by 600 RX- and γ-irradiation was studied by scoring multivalent configurations in descendant spermatocytes by finding that frequencies of 0, 1, 2 translocations per sperMatocyte did not fit a Poisson distribution.
Abstract: The effect of dose-rate on the induction of reciprocal translocations in mouse A type spematogonia by 600 RX- and γ-irradiation was studied by scoring multivalent configurations in descendant spermatocytes. With X-irradiation over a range of dose-rates from 0.8 to 913 R/min there was no significant change in the frequency of affected spermatocytes, which averaged 12.8%. With γ-irradiation, however, there was a steady increase in frequency from 1.4% at 0.02 R/min to 12.1% at 86 R/min, the points fitting a straight line on a semi-log plot. At 0.08 R/min the X-ray yield was twice that for γ-rays. Possible reasons for these differences are discussed. Frequencies of 0, 1, 2 translocations per spermatocyte did not fit a Poisson distribution since there were less then expected in the 1-class, but more in higher classes. This was probably a consequence of differential radiosensitivity of the irradiated spermatogonia, although preferential clonal proliferation may also be involved.
95 citations
TL;DR: Intracellular complexes of UV lesions in DNA with molecules of photoreactivating enzyme (PRE) in E. coli can be photolysed with a probability close to 1 by single light flashes of about 1 millisecond duration, and a heterogeneity of the photoproducts is evident with regard to both complex formation and stability.
Abstract: Intracellular complexes of UV lesions in DNA with molecules of photoreactivating enzyme (PRE) in E coli can be photolysed with a probability close to 1 by single light flashes of about 1 millisecond duration The observed photoreactivation (PR) effect permits the number of PRE-substrate complexes present at the time of the flash to be determined on the following basis: ( a ) The number of PRE-substrate complexes equals the number of lesions repaired; ( b ) The number of photorepairable UV lesions present in DNA equals the number of pyrimidine dimers recoverable from acid hydrolysates; a UV dose of 1 erg·mm −2 of 2537 A radiation causes the formation of approximately 65 dimers per E coli chromosome; ( c ) The observed PR effect can be expressed by the formal “dose-reduction”, ie by the reduction in the number of dimers The kinetics of intracellular complex formation can be followed by varying the time interval between UV irradiation and flash reactivation Stationary phase B s−1 cells, irradiated with 48 erg·mm −2 form a maximum number of complexes within approximately 5 min at room temperature, 50% of them being formed within the first 10–15 sec For greater UV doses (64–24 erg·mm −2 ) the maximum number formed reaches a constant limiting value of 20, indicating that this is approximately the number of PRE molecules in these cells Experiments with sequential flashes at various temperatures between 2° and 44° show that both the maximum extent of complex formation and the photolytic rate constant are temperature-independent in this range Hence, the usually observed temperature-dependence of PR under conditions of continuous illumination reflects the temperature-dependence of the complex formation only Extensive PR effects with single light flashes were also found in UV-irradiated phage T1 after injection of unirradiated B s−1 cells The effects are much smaller in irradiated host cells due to competition by the bacterial DNA Creating the competitive substrate after the phage DNA has reacted with the PRE results in a time-dependent decrease of the PR effect in phage as the enzyme equilibrates between the host-cell and phage DNA's The slow rate of equilibration indicates a relatively high stability of the complexes in the dark A heterogeneity of the photoproducts is evident with regard to both complex formation and stability Comparative experiments with phage infecting other host strains indicate that the number of PRE molecules in strain B/r equals that in B s−1 , but is lower in the K12 derivatives AB 1157, AB 2437 and AB 2480
92 citations
TL;DR: The data on the EMS-induced mutants provide further support for the hypothesis that an AT pair at the mutant site gives rise to polarized or noncomplementing mutants more often than a GC pair atThe mutant site.
Abstract: The genetic alterations in ethyl methanesulfonate (EMS)-induced ad- 3 B mutants of Neurospora crassa have been identified by tests for specific revertibility after treatment with O -methyl-hydroxylamine (OMHA), nitrous acid (NA), ethyl methanesulfonate (EMS), and a monofunctional acridine mustard (ICR-170). Mutants classified as base-pair substitutions reverted after treatment with at least 1 of the first 3 compounds, whereas mutants classified as base-pair insertions or deletions reverted only after treatment with ICR-170. A random sample of 82 EMS-induced ad-3B mutants were analyzed; 76 were characterized by their reversion response, and 6 were excluded because of their high rate of spontaneous reversion or leaky growth. The mutants characterized as to reversion mechanism and type of unidentified genetic alteration consisted of (1) base-pair transitions: AT to GC, 41%, and GC to AT, 17%; (2) base-pair insertions or deletions, 9%; (3) nonrevertible, 7%; (4) mutants which only revert spontaneously and not after treatment with any of the four mutagens, 18%. It is likely that a part of the mutants in the latter class result from a base-pair substitution. Of the mutants which only reverted spontaneously, 13% out of the total of 18% had a nonpolarized complementation pattern and are therefore likely to result from a base-pair substitution. As a result of these considerations, a range from 58% to 79% of the EMS-induced mutants may result from single base-pair substitutions. The correlation between complementation pattern and genetic alteration at the molecular level found previously by us among NA-induced ad-3B mutants was also found within EMS-induced mutants. Mutants with nonpolarized complementation patterns resulted mainly from base-pair substitutions, whereas mutants with polarized complementation patterns and noncomplementing mutants are derived from a variety of genetic alterations. In addition, the data on the EMS-induced mutants provide further support for the hypothesis that an AT pair at the mutant site gives rise to polarized or noncomplementing mutants more often than a GC pair at the mutant site.
91 citations
TL;DR: It is shown here that high intensity flash illumination (duration of the order of 1 millisecond) causes this repair in essentially all enzyme-substrate complexes present at the time, which allows several kinds of studies.
Abstract: The photoenzymatic repair of ultraviolet (UV) lesions in DNA is a photochemical reaction which occurs in an enzyme-substrate complex between these lesions and photoreactivating enzyme (PRE). It is shown here that high intensity flash illumination (duration of the order of 1 millisecond) causes this repair in essentially all enzyme-substrate complexes present at the time. This fact allows several kinds of studies. (1) By applying the flash at timed intervals after mixing PRE and UV-irradiated bacterial transforming DNA, the formation of enzyme-substrate complex can be observed directly. The process takes of the order of minutes for its completion at the usual reaction concentrations, and the effect of changing concentration shows that most of this time is required for the extremely dilute reactants (∼ 10−9M) to encounter each other in solution. (2) When a sequence of flashes is applied with UV lesions in excess, the resulting stepwise repair permits complex formation to be studied at each level of recovery, from the first set of lesions erased to the last. The result shows that the lesions are heterogeneous with respect to rate of complex formation. (3) The rate of complex formation depends on temperature, but once a comples has been formed at 37° it does not rapidly dissociate on shifting the temperature to 2°. Repeating the experiments at lower light intensity, where not all the complexes present are repaired at each flash, then shows that the actual photochemical process in the complex is temperature-independent over the 2–37° range—at least for the most rapidly complexing lesions. (4) When PRE is allowed to complex with irradiated transforming DNA in the dark, and irradiated non-transforming DNA is subsequently added flashes applied at various times after this addition allow the dark dissociation of enzyme-substrate complexes to be followed. Comparison with the converse experiment, in which PRE is first complexed with lesions on non-transforming DNA, shows that some complexes are extremely stable, the enzyme preferentially remaining on the first DNA with which it forms a complex even after 2 h. Complexes with UV lesions on the synthetic polydeoxynucleotides dA:dT and dG:dC are more stable than most of complexes with natural DNA. (5) Measurement of complex formation under conditions of DNA excess, where essentially all the enzyme is bound, permits determination of the number of enzyme molecules relative to the number of UV lesions. The reasonable assumption that the number of lesions equals the number of pyrimidine dimers recoverable from the DNA then gives an absolute count. Provided the molecular weight of 3·104 given by Muhammed is approximately correct, the proportion of pure enzyme to totat protein in crude yeast extract is about 2·10−6.
78 citations
TL;DR: The conclusion is presented that the processes which are responsible for the joining of broken pieces of DNA are present and functional during all phases of the cell cycle, including mitosis, and consistent with the hypothesis that mammalian cell chromosomal DNA is arranged in a series of small units held together by linker molecules which are labile to alkaline conditions.
Abstract: Radiation-induced single strand breaks in the DNA of synchronized Chinese ahmster cells and the rejoining of broken pieces have been investigated by the use of alkaline sucrose density gradients. The weight average molecular weight of denatured DNA has been determined for cells in mitosis, G1 and S phase following irradiation and post-irradiation incubation. The data presented supports the conclusion that the processes which are responsible for the joining of broken pieces of DNA are present and functional during all phases of the cell cycle, including mitosis. The molecular weight of denatured DNA from unirradiated control cells consisted of a wide distribution of small and large pieces ranging from about 10·106 to 250·106 with a weight average molecular weight of 50 to 55·106. This data is consistent with the hypothesis that mammalian cell chromosomal DNA is arranged in a series of small units held together by linker molecules which are labile to alkaline conditions.
76 citations
TL;DR: It was found that the presence of cysteamine during irradiation protected against radiation-induced breaks, being most effective in early S and minimal in G2 phase.
Abstract: The induction and rejoining of single-strand breaks in the DNA of asynchronous and synchronized cultures of human-kidney cells (T-cells) were investigated. The assessment of breaks was carried out with a modified alkaline sucrose-gradient technique. The cells were lysed on top of the gradient in the presence of tri-isopropyl-naphthalenesulphonic acid (TIPNS) and 4-aminosalicyclic acid (PAS). The sedimentation pattern of DNA was studied after X-irradiation with doses up to 40 krad. Breaks could be detected by irradiating cells with doses higher than 5 krad. With synchronous cell populations the smallest induction of breaks was found in the DNA of cells in progress from late S to early G2. More breaks were induced in early S and G1. The rejoining of breaks in the DNA was studied during incubation of the cells at 37° after X-ray exposures to 5 and 20 krad. The capacity of rejoining breaks seemed to fluctuate slightly in the different phases of the cell cycle, being most effective in early S and minimal in G2 phase. In preliminary experiments, carried out to study the influence of protective agents, it was found that the presence of cysteamine during irradiation protected against radiation-induced breaks.
74 citations
TL;DR: The marked changes in RNA synthesis during growth of the oocyte are considered as an indicator of general metabolic activity, and the possible relationships to stage differences in sensitivity to radiation-induced cell killing and mutation are discussed.
Abstract: Hybrid female mice (101 × C 3 H) were injected intraperitoneally with 75 μC of [ 3 H]uridine and killed at intervals ranging from 15 min to 15 days. Autoradiographs of 3 μ sections revealed rapid nucleolar and nuclear labeling with subsequent transfer of label to the cytoplasm in growing oocytes. Uptake of [ 3 H]uridine ceased at about the time of antrum formation; oocytes with a well-developed antrum showed no [ 3 H]uridine incorporation. Labeling was removed by RNAase + cold TCA, and it was assumed that [ 3 H]-uridine incorporation represented synthesis of ribosomal and messenger RNA which was stored in the cytoplasm in preparation for subsequent cleavage. The marked changes in RNA synthesis during growth of the oocyte are considered as an indicator of general metabolic activity, and the possible relationships to stage differences in sensitivity to radiation-induced cell killing and mutation are discussed.
64 citations
TL;DR: The radicals formed in this reaction inactivate DNA and these compounds, as well as carbamates that can be enzymatically converted to reactive N -hydroxycarbamates, may therefore cause chromosomal breaks and mutations.
Abstract: Antidepressant hydrazines (e.g. isocarboxazid, nialamide, and phenelzine) and the anti-tubercle agent isoniazid react with oxygen, producing hydrogen peroxide. The radicals formed in this reaction inactivate DNA. These compounds, as well as carbamates that can be enzymatically converted to reactive N-hydroxycarbamates, may therefore cause chromosomal breaks and mutations.
TL;DR: The difference in the frequency of the GC pairs at mutant sites among the three different classes of complementation response indicates that nonsense mutations occur more frequently among mutants with polarized complementation patterns and among noncomplementing mutants than among mutantsWith nonpolarized complemented patterns.
Abstract: Nitrous acid-induced ad-3B mutants of Neurospora crassa were tested for revertibility after treatment with hydroxylamine (HA). Mutants which reverted after the treatment were classified as having guanine-cytosine (GC) at the mutant site. A high frequency (86.5%) of nitrous acid-induced ad-3B mutants resulting from base-pair transitions have GC at the mutant site, whereas in bacteriophage T 4 most nitrous acid-induced rII mutants have adenine-thymine (AT) at the mutant site. This apparent contradiction is discussed. In a random sampling of base-pair transition ad-3B mutants, we found among mutants with nonpolarized complementation pattern a lower incidence (2.3%) of AT at the mutant site than among mutants with polarized complementation pattern (25.0%) and among noncomplementing mutants (55.0%). Nonsense mutants, which specify the RNA triplets UAA, UAG, or UGA, and presumably the DNA anticodons ATT, ATC or ACT, should not be able to revert by a GC → AT transition, because by reaction with hydroxylamine the two C-containing triplets would be transformed to ATT, a nonsense triplet. The difference in the frequency of the GC pairs at mutant sites among the three different classes of complementation response indicates that nonsense mutations occur more frequently among mutants with polarized complementation patterns and among noncomplementing mutants than among mutants with nonpolarized complementation patterns.
TL;DR: Results indicate that in E. coli B/r under usual irradiation conditions PER repairs preferentially UV lesions that would otherwise be dark-repaired; in fact, all of the photo-repairable lesions inE.
Abstract: Photoenzymatic repair (PER) immediately after UV irradiation of E. coli B/r abolishes approximately 67% of those UV lesions that usually do not become dark repaired (PR sector = 0.67). If the irradiated cells are held in bufer before undergoing PER, the PR sector decreases and becomes virtually zero after 24–48 h holding. Such an effect is essentially absent in the E. Coli strains Bs−1, AB 2437, and AB 2480 which are deficient in excision-resynthesis dark repair (ERR). In B/r, the decrease in the PR sector is much inhibited in the presence of potassium cyanide, caffein, and acriflavine. These and other results suggests that the observed loss of photoreactivability by holding in buffer is due to excision of photorepairable lesions. However, the fact that the decrease in PR sector is the result not only of an increase in dark survival (“liquid-holding recovery”), but also of a decrease in the absolute level of PR survival indicates that excision does not always lead to dark repair. Loss of photoreactivability during holding is only partial in strain AB 2463 (rec−, which is deficient in another type of dark repair (“REC repair”), and in E. coli B. No PR is observed in B/r cells UV-irradiated at an extremely low dose-rate (where they are known to undergo most extensive dark repair), while under the same conditions a reduced amount of PR is still found in AB 2463 (rec−) cells. Altogether, the results indicate that (1) in E. coli B/r under usual irradiation conditions PER repairs preferentially UV lesions that would otherwise be dark-repaired; (2) in fact, all of the photo-repairable lesions in E. coli are dark-repairable; and (3) complete dark repair of photo-repairable lesions in B/r requires both REC repair and a higher-than-normal extent of ERR.
TL;DR: Allelism tests performed between X-ray-induced lethals that were located on the X-chromosome of Drosophila at a region covered by the Y.ma-l + translocation suggest new approaches to the study of the organization of the genetic material in chromosomes and the nature of various mutational events.
Abstract: Allelism tests were performed between X-ray-induced lethals that were located on the X-chromosome of Drosophila at a region covered by the Y.ma-l + translocation. The complementation map which was constructed from the matrix of allelic combinations proved to be linear. So far 20 sections, or functional units, have been delineated. Further analysis should increase the number of sections until each section comprises one cistron. Practically all post-meiotic X-ray induced lethals in the region were aberrations. It is inferred that visible mutations induced by X-rays were deficiencies at non-essential loci. The breakage points of mutations in the segment were not distributed at random. The “hot spot” was attributed to an intercalary heterochromatic band, which by pairing with the adjacent proximal heterochromatin caused preference in breaks simultaneously at the “hot spot” and the proximal heterochromatin, and hence also caused preference for extensive aberrations. A correlation was found between male sterility and heterochromatic aberrations, but not between male sterility and X:A translocations. This kind of analysis suggests new approaches to the study of the organization of the genetic material in chromosomes and the nature of various mutational events.
TL;DR: Compared the distributions of breakage-reunion events in rye genotypes which have very different patterns of chiasma distribution indicate a marked similarity in the distribution patterns of these two events, suggesting that they are causally related and that they may therefore represent different manifestations of the same basic process.
Abstract: Bridges and fragments at meiotic anaphase stages resulting from the spontaneous breakage and reunion of chromatids are common in genotypes of rye which are genetically unbalanced as a result of inbreeding or hybridisation. Similar configurations have been described in a variety of other plant and animal species, and ascribed to the same cause. Attention is drawn to the many similarities of the postulated breakage-reunion event to the exchange process involved in meiotic crossing-over, and the question is asked whether this anomalous behaviour could result from errors in crossing-over. Previous work employing different species having characteristically different and localised patterns of chiasma distribution has suggested the presence of a correlation between the distribution of chiasmata and the distribution of breakage-reunion events within bivalents. In the present investigation this approach has been followed, and extended, by comparing the distributions of breakage-reunion events in rye genotypes which have very different patterns of chiasma distribution. The results obtained indicate a marked similarity in the distribution patterns of these two events, suggesting that they are causally related and that they may therefore represent different manifestations of the same basic process.
TL;DR: The absence of small deletions induced by ethyleneimine indicates as essential difference in the mechanisms by which such aberrations and larger breakage-related rearrangements are produced, leading to the hypothesis that the inability to produce such changes represents a major qualitative difference between the effects of monofunctional and multifunctional alkylating chemicals.
Abstract: A comparison was made of the frequencies of X-chromosome recessive lethals and translocations involving the Y, II, and III chromosomes induced in mature spermatozoa by ethyleneimine and ethyl methanesulfonate. The frequency of lethals induced by the imine was found to be twice that induced by the mesyloxy ester, based on experiments in which comparable concentrations of the two chemicals were injected. The immune was found to be a relatively effective chromosome-breaking agent, whereas only a single translocation was detected in more than 2000 EMS-treated gametes tested; indicating a marked difference either in the sites or the consequences of alkylation by the two chemicals. The feeding of EMS to adult males was found to result in 10-fold increase in the frequency of induced lethals and a pronounced increase in translocation frequency. The determination of gross aberrations and small deficiencies associated with 50 ethylenimine- and 45 ethyl methanesulfonate-induced lethals was made from salivary-gland chromosome preparations of heterozygous female larvae. 9 of the imine-induced lethals were found to be associated with gross changes, including two 3-break rearrangements and one involving 2 breaks in both the X and III chromosomes. For none of the 95 lethals examined cytologically was evidence found of associated small deficiencies; whereas such changes clearly have been established to result from alkylation with multifunctional compounds and to be induced by ionizing radiations. The absence of small deletions induced by ethyleneimine indicates as essential difference in the mechanisms by which such aberrations and larger breakage-related rearrangements are produced. Moreover, the absence also of small deletions induced by ethyl methanesulfonate leads to the hypothesis that the inability to produce such changes represents a major qualitative difference between the effects of monofunctional and multifunctional alkylating chemicals.
TL;DR: The results indicate that, in contrast to the lesions induced by X-rays, those induced by certain radiomimetic chemicals require the intervention of chromosome replication (or DNA synthesis) before they can be converted to chromosomal aberrations observable at mitosis.
Abstract: When mitotically proliferating cells are X-irradiated, chromosome structural changes are found, at the first (T 1 ) mitotic division after irradiation, in cells which were in all stages of the mitotic cycle at the time of treatment. On the other hand, after treatment of cells with certain radiomimetic chemicals such as maleic hydrazide (MH) or alkylating agents, chromosomal aberrations at T 1 mitosis are only found in those cells which were synthesising DNA (S cells) and those in the pre-synthetic (G 1 ) phase of the time when these agents were applied; cells in the post-synthetic (G 2 ) phase at the time of treatment contain no aberrations at their T 1 mitosis but do so at T 2 mitosis 11, 12, 45 . These results indicate that, in contrast to the lesions induced by X-rays, those induced by certain radiomimetic chemicals require the intervention of chromosome replication (or DNA synthesis) before they can be converted to chromosomal aberrations observable at mitosis. In view of the difference between the lesions induced by these agents, an experiment was performed in order to determine whether or not such lesions are able to interact with one another in the formation of aberrations. In the experiment reported here Vicia faba roots were treated with X-rays, MH, or X-rays+ MH, and [ 3 H]thymidine autoradiography was used as a “marker” for the mitotic cycle. The results indicate that, after the combined X-ray/MH treatment, the frequency of all types of chromosomal aberration, at all stages of the mitotic cycle, is merely the sum of the frequencies induced by X-rays and MH when given separately. No evidence was obtained of any interaction between lesions induced by these two agents. This result is completely at variance with the conclusions of others and this is thought to be due to the fact that other workers have made observations at only a limited number of times after treatment and have not adequately taken into account the differential mitotic delay induced by these agents. It is suggested that the lack of interaction is due to the fact that, whereas the lesions induced by X-rays are available for interaction for a short period of time immediately after irradiation, those induced by MH cannot interact until the chromosomes, in which they have been induced, undergo replication. Thus there is a temporal barrier to interaction, since the times, after treatment, when the lesions induced by these two agents are available for interaction, do not coincide.
TL;DR: It is suggested that the UV induced changes in the nucleic acids (at a relatively low dose level) mainly interfere with DNA replication in S phase and do not or only slightly inhibit progression through other parts of the cell cycle.
Abstract: Exposure of living cells to ultraviolet light in the 254 mμ range leads to photochemical changes in the nucleic acids. The influence of these changes on progression through the division cycle was investigated using two different cell lines: a heteroploid epithelial cell line of human kidney origin (T cell) and a diploid chinese hamster fibroblast (DON cell). The duration of the cell cycle of these lines was 24–26 and 10–12 h respectively. Synchronous and asynchronous cultures were used. Cells irradiated in late G 2 phase with doses of 100 erg/mm 2 or less were not or only slightly delayed in entering mitosis. Mitotic delay increased when the cells were irradiated earlier in G 2 . Exposure in S phase was followed by an inhibition of DNA synthesis, leading to a lengthening of S (4–5 h after a dose of 35 erg/mm 2 ) and delay of cell division. This inhibition increased if irradiation was carried out earlier in S phase. After exposure of T cells in G 1 phase, which has a relatively long duration, the cells started earlier with [ 3 H]thymidine incorporation. This incorporation indicates a shortening of G 1 phase rather than an unscheduled synthesis of DNA. In general these data suggest that the UV induced changes in the nucleic acids (at a relatively low dose level) mainly interfere with DNA replication in S phase and do not or only slightly inhibit progression through other parts of the cell cycle.
TL;DR: Observations suggest that terminal deletions originate from two-hit events, in accord with Revell's 18–21 explanation of the origin of chromatid deletions, rather than from single breaks as proposed on the “breakage first” 28 model.
Abstract: Regression analyses of the dose-response curves of radiation-induced chromosome aberrations in blood cells of Wallabia bicolor (2 n = 11) show that the kinetics of yield of terminal deletions, as well as classical two-lesion aberrations (rings, dicentrics, and intercalary deletions), best fit the model, Y = a + cD 2 . In addition, all aberrations, including terminal deletions, respond to a fractionated dose in the way expected of two-hit aberrations. These observations suggest that terminal deletions originate from two-hit events. It is proposed that they result from incomplete exchanges, in accord with Revell's 18–21 explanation of the origin of chromatid deletions, rather than from single breaks as proposed on the “breakage first” 28 model.
TL;DR: The frequency of intragenic mitotic recombination (gene conversion) induced by UV light was greater among survivors in the sensitive strains compared to wild-type controls, but was less when compared in terms of equal survival.
Abstract: Intergenic and intragenic recombination during vegetative growth and at meiosis has been studied by selective plating techniques in diploid strains of yeast homozygous for alleles of six genes governing sensitivity to ultraviolet radiation. The following results were obtained: 1. ( 1 ) None of the uvs mutations caused a significant increase in spontaneous mitotic intragenic recombination. 2. ( 2 )The frequency of intragenic mitotic recombination (gene conversion) induced by UV light was greater among survivors in the sensitive strains compared to wild-type controls, but was less when compared in terms of equal survival. 3. ( 3 ) The dose-response curves for UV-induced mitotic recombination between the locus of a gene and its centromere were complex, but in most cases the uvs diploids showed a greater response than the controls. 4. ( 4 ) No differences from the controls were found in the frequency of intragenic or intergenic recombination at meiosis, but significant differences were found between certain uvs strains.
TL;DR: In the haploid fission yeast Schizosaccharomyces pombe caffeine supplementation of the plating medium leads to a decreased survival following UV irradiation, suggesting that the caffeine-sensitive dark-repair system is specific for only some types of lesion.
Abstract: In the haploid fission yeast Schizosaccharomyces pombe caffeine supplementation of the plating medium leads to a decreased survival following UV irradiation. In a met − → met + reversion system in which the revertants are due to suppressor mutations there is a differential enhancement of lethality and of met + reversions by caffeine. This result may mean that potentially lethal and potentially mutagenic lesions are different. They could differ either in their chemical nature, or in their accessibility to a caffeine-sensitive dark-repair system. Caffeine is without any obvious effect on the lethality and met + reversions induced by nitrous acid or nitrosomethylurethane treatments. This suggests that the caffeine-sensitive dark-repair system is specific for only some types of lesion.
TL;DR: The interpretation that the amount of repair in sperm depends on different levels of available energy is supported by the observation that NaF pre-treatment is still effective in increasing the mutation frequency over that in the controls, when N 2 was given before, during and after irradiation.
Abstract: The effect of two inhibitors of glycolysis, NaF and iodoacetamide on the production of recessive lethal mutations by X-rays in mature Drosophila sperm has been investigated. Pre-treatment with NaF resulted in a consistent and highly significant increase of the mutation frequency. This effect is thought to result from interference with a repair process which makes use of energy produced by glycolysis, and does not arise from an increase of the oxygen tension. When the action of NaF was studied in combination with pre- and post-treatments with N2 and O2, it was observed: (1) that irrespective of pre-treatment with N2 or O2, NaF enhanced the mutation frequency over that in the saline controls; (2) that following irradiation under anoxia, post-treatment with N2 reduced the mutation frequency below that observed with O2 post-treatment, even when the flies had been pre-treated with NaF. These additive effects of NaF pre-treatment and O2 post-treatment have been taken as an indication that, even when glycolysis is inhibited by NaF, some energy is left, which is still available for repair by post-radiation anoxia. This interpretation that the amount of repair in sperm depends on different levels of available energy is supported by the observation that NaF pre-treatment is still effective in increasing the mutation frequency over that in the controls, when N2 was given before, during and after irradiation. Thus repair is maximal with NaClN2RN2, intermediate with NaFN2R2N2, and minimal with NaFN2RO2. Pre-treatment with iodoacetamide gave more variable results than that with NaF.
TL;DR: Cultures of mammalian cells exposed to ionizing radiations give rise to a large proportion of surviving cells which express radiation injury in an heritable manner, in that isolated progency of irradiated cells that give Rise to abnormally small colonies are found to grow more slowly and are more sensitive to further irradiation.
Abstract: Cultures of mammalian cells exposed to ionizing radiations give rise to a large proportion of surviving cells which express radiation injury in an heritable manner, in that isolated progency of irradiated cells that give rise to abnormally small colonies are found to grow more slowly and are more sensitive to further irradiation Such inherited injury occurs in irradiated human as well as hamster cell lines In two defective cell lines investigated, the enhanced radiation sensitivity was accompanied by reduced oxygen consumption Defective Chinese hamster cell lines can exist with no visible gross alterations in karotype The frequency of small colony appearance in irradiated normal cultures increases regularly with dose, and the frequency with which they are produced is apparently too great to be due to single-gene mutations
TL;DR: A new karyotype of Vicia faba with all 12 chromosomes easily interdistinguishable has been used to study the interchromodomal distribution of chromatid aberrations induced by ethyl alcohol and maleic hydrazied.
Abstract: A new karyotype of Vicia faba with all 12 chromosomes easily interdistinguishable has been used to study the interchromodomal distribution of chromatid aberrations induced by ethyl alcohol and maleic hydrazied. The distribution patterns of intra- and interchanges induced by ethyl alcohol and maleic hydrazide are non-random and agent-specifc. These patterns are neither changed by pretreatment with EDTA which sensitizes the cells to both agents nor by scoring aberrations after different recovery times. The preferential participation in aberrations of individual chromosome segments which is responsible for the non-random and agent-specific distribution of aberrations between chromosomes is a transposable feature of the segments in question. The transfer of such a segment to another position within the karyotype is accompanied by a corresponding shift in aberration distribution. In addition to ethyl alcohol- and maleic hydrazide-specific patterns of distribution of chromatid aberrations, particular chromosomes and chromosome segments have been found to be involved with differing frequencies in particular types of aberration after both ethyl alcohol and maleic hydrazide treatment. This is understood as being due to factors which, secondarily and differentially, influence the type of interaction of lesions preferentially induced in the relevant chromosomes and chromosome segments.
TL;DR: All acridines inactivate T4B phages, but a wide variation is found in their efficiency: 9-aminoacridine The action of methylene blue, the strongest inactiviting dye, does not appear to be similar to the acridine reaction.
Abstract: The action of visible light on suspensions of coliphage T4B sensitized with a dye was studied by examining the loss of infectivity, the increase of r mutants among the survivors and the induction of free radicals in the phage nucleic acid. The dyes selected were five different acridines and three structurally related substances: pyronin, acridine red and methylene blue. Phages were always kept in phosphate buffer pH 6.5, ionic strength 0.1; the dye was allowed to equilibrate with the phage for 20 h at 37° in the dark, and the irradiation was done on the 100-times diluted complex. The kinetics of all inactivations observed are exponential. With proflavine, a relationship is established between the inactivation constant and the dye concentration. All acridines inactivate T4B phages, but a wide variation is found in their efficiency: 9-aminoacridine The action of methylene blue, the strongest inactiviting dye, does not appear to be similar to the acridine reaction. The mutagenic activity of proflavine (concentration up to 3·10−5M is directly proportional to inactivation with an increase of 0.73±0.08·10−3 in the r (r+r + ) ratio per lethal hit. As far as the other dyes are concerned this effect is of the same magnitude except that of 9-aminoacridine which is lower. The energy absorbed by the bound dye and transferred to DNA must lead to a lesion or lesions which either destroy the phage infectivity or give rise to mutations.
TL;DR: Treatment of barley seeds pre-soaked in water for different periods ranging from 8 to 40 h with ethyl methanesulphonate (EMS) and N -nitrosomethyl urea (NMU) showed that the seeds were most sensitive to mutagenic treatments at 16 h and 28 h from the beginning of pre- soaking.
Abstract: Treatment of barley seeds pre-soaked in water for different periods ranging from 8 to 40 h with ethyl methanesulphonate (EMS) and N -nitrosomethyl urea (NMU) showed that the seeds were most sensitive to mutagenic treatments at 16 h and 28 h from the beginning of pre-soaking. Autoradiographic studies revealed that the first incorporation of labelled thymidine occurs after 16 h of pre-soaking. Therefore, the first peak of sensitivity may be related with DNA synthesis. The second peak of sensitivity may be caused either by the release of certain metabolic products which have a sensitizing effect or because of a second wave of cells entering DNA synthesis in cases as asynchronous cell division. The plants in the M 1 generation showed a high frequency of chlorophyll chimeras. The frequency of appearance as well as the size of these sectors were significantly high after treatment with NMU. Multiple mutations also occurred more frequently in NMU-treated plants. There is great scope for increasingly both the frequency and spectrum of mutations in treatments with chemical mutagens through suitable modification of the treatment conditions.
TL;DR: A mutant of Aspergillus nidulans has been isolated which shows greater sensitivity to ultraviolet irradiation and nitrous acid treatment than the strain from which it was derived.
Abstract: A mutant of Aspergillus nidulans has been isolated which shows greater sensitivity to ultraviolet irradiation and nitrous acid treatment than the strain from which it was derived. The mutation conferring mutagen sensitivity is inherited as a single recessive nuclear gene. Matings which were heterozygous for the mutation exhibited normal recombination between linked markers. Mating homozygous for the sensitivity mutation yielded sterile, dwarf cleistothecia. Heterocaryons in which both of the components carried the sensitivity mutation failed to form somatic diploids.