Showing papers in "Mutation Research in 1970"
918 citations
TL;DR: Effective mutagenesis in Streptomyces requires a longer and more intense treatment than in some other microbes; suitable conditions are described.
Abstract: Mutagenesis was tested by the reversion of several auxotrophic mutations and by the induction of auxotrophs. Mutagenesis at alkaline pH was quantitatively related to the release of an unstable, mutagenic intermediate of NTG decomposition, presumably diazomethane. No evidence was obtained for mutagenesis by undecomposed NTG at pH 5. At very acid pH (2.5), there was weak mutagenesis, associated with high lethality, presumably by a different mechanism from that operating at alkaline pH. Effective mutagenesis in Streptomyces requires a longer and more intense treatment than in some other microbes; suitable conditions are described.
167 citations
TL;DR: Primary fibroblast cultures were established from 8 patients having different degrees of clinical symptoms of xeroderma pigmentosum, suggesting a genetically determined constant level of reduced repair replication.
Abstract: Primary fibroblast cultures were established from 8 patients having different degrees of clinical symptoms of xeroderma pigmentosum. Repair replication after exposure of cells to different doses of ultraviolet irradiation (predominantly 254 nm) was studied by means of [ 3 H] thymidine labeling and autoradiography. A decreased repair DNA synthesis in cells in G 1 and G 2 phase was found in all xeroderma pigmentosum cell cultures relative to control cell cultures obtained from healthy people. Cell strains originating from two severe cases of xeroderma showed no repair synthesis after short autoradiographic exposure times, although, after one-month exposure a slight labeling was observed (10–20% of the control). The repair activity in cells from the other patients ranged from 70% for a light case to 50 and 30% for moderate cases of the disease. Cells obtained from related patients showed identical levels of repair activity, suggesting a genetically determined constant level of reduced repair replication. A xeroderma cell strain transformed by SV 40 virus showed no repair replication as did the original strain before transformation.
151 citations
TL;DR: 8-MOP may represent a new type of antimutagen for suppressor mutations arising from potentially excisable damage in Escherichia coli WP2, similar to that for far ultraviolet light alone although there are some differences.
Abstract: Suppressor mutations and true reversions of Escherichia coli WP2 were produced in roughly equal numbers by near ultraviolet light (NUV) (≈ 360 nm) in the presence of 8-methoxypsoralen (8-MOP). Both types of mutation are probably the result of base-pair transitions. Neither NUV nor 8-MOP was mutagenic by itself. Both premutational and potentially lethal damage produced by 8-MOP plus NUV was in the DNA and largely excisable as judged by the comparative sensitivities of strains possessing and lacking excision-repair capacity. It was not photoreactivable. A “reckless” Rec- strain was sensitive to the lethal effect of 8-MOP plus NUV and was not detectably mutable; mutability was also lacking in an Exr- mutant. The mechanism of mutagenesis is thus similar to that for far ultraviolet light alone although there are some differences, indicated by the much smaller proportion of suppressor mutants and by the very small “broth effect”, which are largely attributable to an independent physiological effect of 8-MOP and, to a lesser extent, NUV. 8-MOP may represent a new type of antimutagen for suppressor mutations arising from potentially excisable damage.
136 citations
TL;DR: There appears to be a relationship between the degree of repair synthesis and on the other hand frequency of cells entering S-phase, incidence of metaphase plates with chromatid breaks, flow of cells from G2 into pro-metaphase and “uncoiling” of metaphases chromosomes or heterochromatic segments of interphase nuclei.
Abstract: The oncogenic and mutagenic 4-nitroquinoline 1-oxide (4NQO) induces DNA-repair synthesis (unscheduled DNA synthesis) in diploid, aneuploid, normal and neoplastic human and Syrian-hamster cells. DNA-repair synthesis occurs in nuclei at G1, G2 and S-phase and in metaphase chromosomes of Syrian-hamster cells exposed to 4NQO. DNA-repair synthesis was separated from DNA-replication synthesis associated with chromosome replication at S-phase by arginine deprivation. The degree of [ 3 H]TdR incorporation into nuclear DNA is dependent on the dose of 4NQO (5·10 −8 to 1·10 −5 M ) and on the amount of DNA per cell. The time course of DNA-repair synthesis induced by 4NQO or UV was examined on non-dividing cells which were arrested by an arginine-deficient culture medium: an early occurring peak is followed by an abrupt decline at about 8 h post-treatment which is succeeded by a prolonged low level incorporation of [ 3 H]TdR. The effect of a completed and uncompleted repair synthesis on the flow of cells into S-phase and on the frequency of chromosome anomalies was studied on cells arrested by arginine deprivation and triggered to divide by addition of arginine. There appears to be a relationship between the degree of repair synthesis and on the other hand frequency of cells entering S-phase, incidence of metaphase plates with chromatid breaks, flow of cells from G2 into pro-metaphase and “uncoiling” of metaphase chromosomes or heterochromatic segments of interphase nuclei.
120 citations
TL;DR: A comparison of induced mutation rates for various species and cells after ionizing irradiation shows that the high mutability of animal cells compared with microorganisms does not appear to be correlated with the presence of meiotic stages but may be a general property ofAnimal cells.
Abstract: The mutation of cultured Chinese hamster cells to 8-azaguanine resistance has been studied after ultraviolet and X-irradiation. Optimum numbers of induced mutants appeared after an expression time of 30–40 h before the addition of 8-azaguanine, and the yield of mutants tended to decrease when the initial number of cells in a 9 cm diameter plate exceeded 105. There was some evidence consistent with the hypothesis that cells resistant to 8-azaguanine are at a disadvantage at high cell densities in the absence of 8-azaguanine. An incubation period of at least 10 days after the addition of 8-azaguanine was necessary to detect the maximum number of induced mutants. Dose-response curves after exposure to ultraviolet light were linear in contrast to cumulative-type curves obtained after X-irradiation. A comparison of induced mutation rates for various species and cells after ionizing irradiation shows that the high mutability of animal cells compared with microorganisms does not appear to be correlated with the presence of meiotic stages but may be a general property of animal cells. The high mutability per unit dose of ionizing radiation, although not totally incompatible with a theory of DNA-located primary damage, could indicate that the “target” is large, for example a lysozome which when “hit” releases DNA-damaging enzymes through the nucleus. The results are discussed in terms of possible mechanisms and of the suitability of the system for routine mutagen screening.
110 citations
TL;DR: Blood samples obtained from patients with various types of inborn chromosome abnormalities were exposed to γ-rays and the relationship between the chromosome constitution and chromosomal radiosensitivity of lymphocytes was studied, showing that the trisomic cells are particularly cancer-prone and that the illegitimate repair of chromosome damage, which is intrinsic to the tr isomic cells, may play an important role in the development of cancer.
Abstract: Blood samples obtained from patients with various types of inborn chromosome abnormalities were exposed to γ-rays and the relationship between the chromosome constitution and chromosomal radiosensitivity of lymphocytes was studied by analysing types and frequencies of radiation-induced chromosome aberrations. The results showed that the chromosomal radiosensitivity was consistently higher in the cells which were trisomic for the whole or a part of a chromosome than in the cells with normal karyotype, but it was not significantly influenced by the monosomic conditions, reciprocal translocation and inversion. Age of the subjects also affected the chromosomal radiosensitivity, which was elevated in the neonates. The analysis of chromosome aberrations showed that the high frequency of radiation-induced chromosome aberrations was due to the increased production of exchange aberrations and that the level of deletions was not affected either by factors of the chromosome constitution or of the age of the subject. A hypothesis to explain the increased chromosomal radiosensitivity of the trisomic cells was given in line with the effects of altered enzyme activity on the production of exchange aberrations. The parallelism between the increased chromosomal radiosensitivity in the trisomic cells and the susceptibility of the affected persons to neoplasia allowed us to recognize that the trisomic cells are particularly cancer-prone and that the illegitimate repair of chromosome damage, which is intrinsic to the trisomic cells, may play an important role in the development of cancer.
110 citations
TL;DR: The studied nitrosoureas do not seem to exert their toxic action by alkylation of proteins but more probably either by a genetical mechanism or by other effects operating at a low nucleophilicity, n, as in the group of methanesulphonates.
Abstract: The rates of reaction ofN-methyl-N-nitrosourea (MNU) and N-ethyl-N-nitrosourea (ENU) with various nucleophiles at pH 8 and 25° were measured and the substrate constants s were estimated to be 0.42 for MNU and 0.26 for ENU. The toxic and mutagenic action of the two nitrosoureas in Arabidopsis thaliana were compared with these s-values. The high mutagenic efficiency is connected with low s-values, as in the group of methanesulphonates. In contrast to a great number of methanesulphonates, 1,2-epoxides, etc., with s higher than 0.5, the studied nitrosoureas do not seem to exert their toxic action by alkylation of proteins but more probably either by a genetical mechanism or by other effects operating at a low nucleophilicity, n. The relative mutagenic effectiveness agrees with alkylation rates at n ≈ 3.
79 citations
TL;DR: Results suggest that the xeroderma strains investigated were deficient in the enzyme(s) involved in the excision of pyrimidine dimers from the DNA.
Abstract: Repair replication and rejoining of single-strand breaks after X-irradiation in human-skin fibroblasts from normal donors and several patients with xeroderma pigmentosum have been compared. The xeroderma strains showed different levels of repair replication following UV exposure. Repair replication and rejoining of breaks, which are considered to be part of the repair mechanism after damage due to X-irradiation and UV-irradiation, appeared to be performed in all xeroderma pigmentosum strains tested to the same level as in control strains. These results, and the observation that in the same xeroderma pigmentosum strains repair replication after UV irradiation was considerably reduced, suggest that the xeroderma strains investigated were deficient in the enzyme(s) involved in the excision of pyrimidine dimers from the DNA.
73 citations
TL;DR: Fungicides tested for genetic activity on diploid cells of the ascomycete Saccharomyces cerevisiae induced mitotic gene conversion and induced cytoplasmic respiratory-deficient mutation at frequencies close to 100%.
Abstract: 14 fungicides have been tested for genetic activity on diploid cells of the ascomycete Saccharomyces cerevisiae. The test system used was induction of: (1) mistotic gene conversion at 2 different loci; and (2) cytoplasmic respiratory-deficient mutants. 2 fungicides turned out to be strongly active in inducing mitotic gene conversion when applied as commercial preparations: Ortho-phaltan (N-(trichloromethylthio)phthalimide) and Polyram-combi (ammonia complex of zinc ethylenebis-(dithiocarbamate) and polyethylenebis(thiocarbamoyl)disulfide). Cignolin (1,8-dihydroxyanthranole), used in dermatology, did not induce mitotic gene conversion but induced cytoplasmic respiratory-deficient mutation at frequencies close to 100%. With 4 more fungicides only a week apparent induction of gene conversion could be observed: Antracol (zinc propylenebis(dithiocarbamate)), Basfungin (ammonia complex of zinc propylenebis (dithiocarbamate) and polypropylenebis(thiocarbamoyl)-disulfide), Dithane-Ultra (manganese-zinc ethylenebis(dithiocarbamate) complex) and Captan (N-(trichloromethylthio)-4-cyclohexene-1,2-dicarbaximide).
TL;DR: The data are consistent with the hypothesis that dimer excision accounts for loss of photoreversibility of stable reversions to tryptophan independence but that DNA replication is necessary to this process for suppressor mutations of this requirement subject to mutation frequency decline.
Abstract: The loss of photoreversibility of UV-induced mutations to tryptophan independence in a tryptophan-requiring strain of E. coli (left after “ mutation frequency decline ”, produced by incubation in the absence of the amino acid, has eliminated most suppressor mutations) occurs during the first 20 min of postirradiation incubation. It is amino acid independent but is blocked by dinitrophenol. It is independent of DNA replication since it occurs in the presence of nalidixic acid, an inhibitor of DNA replication. Loss of photoreversibility of the suppressor mutations (subject to mutation frequency decline ) occurs in correlation with the initial doubling of DNA in the culture and may be prevented by nalidixic acid, suggesting that DNA replication is required for such loss. The initial postirradiation replication of DNA is significant to the mutation process since expression of both sorts of mutation (measured on tryptophan-free minimal agar medium) does not occur unless DNA synthesis is allowed before plating and is prevented by nalidixic acid. The data are consistent with the hypothesis that dimer excision accounts for loss of photoreversibility of stable reversions to tryptophan independence but that DNA replication is necessary to this process for suppressor mutations of this requirement subject to mutation frequency decline .
TL;DR: Experiments in which the reaction-rate constants for the formation of enzyme-substrate complexes and dark dissociation of the complexes, and the photolytic constant for the light-dependent repair step have been determined in E. coli B s−1 are described.
Abstract: It was shown earlier that the use of intense light flashes permits analyzing in greater detail the reaction steps involved in photoenzymatic repair (PER). This paper describes experiments in which the reaction-rate constants for the formation of enzyme-substrate complexes ( k 1 ) and dark dissociation of the complexes ( k 2 ), and the photolytic constant ( k p ) for the light-dependent repair step have been determined in E. coli B s−1 . All three reactions are heterogeneous with respect to these constants. Presumably this reflects the diversity of pyrimidine dimers in irradiated DNA, all of which serve as substrate for photoreactivating enzyme (PRE); the following values are weighted averages. At room temperature, k 1 equals 1.8·10 −3 cell volumes·molecules −1 ·sec −1 , which for a cell volume of 10 −15 liter corresponds to 1.1·10 6 liter·mole −1 ·sec −1 . For k 2 , values ranging from 1.9·10 −3 to 1.3·10 −2 sec −1 have been obtained in different experimental approaches, depending on which criteria were used. k p has been determined under conditions where all of the substrate is complexed with photoreactivating enzyme at the beginning of the illumination. For the wavelengths 385, 366, and 355 nm k p values of, respectively, 1.75·10 −3 , 1.37·10 −3 , and 1.13·10 −3 mm 2 ·erg −1 , have been obtained. From the values the product of ϵ (the molar extinction coefficient of the enzyme-substrate complexes) and Φ (the quantum yield of the photolytic reaction) can be calculated. At the most effective wavelength (385 nm), ϵΦ equals 2.4·10 4 liter·mole −1 ·cm −1 , indicating that both ϵ and Φ must be high. ϵ must be ⩾2.4·100 4 l liter·mole −1 ·cm −1 , since Φ cannot exceed 1; Φ is probably between 10 −1 and 1, since ϵ values >10 5 are unlikely. k 1 and k 2 show positive temperature dependence in the range 5 to 37°, corresponding to activation energies of 11 kcal·mole −1 and about 4.5 kcal·mole −1 for the respective steps, while k p was earlier shown to be essentially temperature-independent in this range.
TL;DR: There was direct relationship between the degree of sensitivity and state of cell division in mutant cells; cells in log phase were highly sensitive, but cells in stationary phase were relatively insensitive.
Abstract: Bacterial recombinationless ( rec ) mutants were killed by a variety of household and photo lamps, emitting wavelengths in both the long UV and visible range There was direct relationship between the degree of sensitivity and state of cell division in mutant cells; cells in log phase were highly sensitive, but cells in stationary phase were relatively insensitive Exclusive of oxygen protected cells from damage Light-sensitive mutants displayed normal photoreactivation after 2537 A UV irradiation
TL;DR: When the two cell lines were plated in caffeine-containing medium immediately after UV irradiation, there was no reduction in the surviving fraction of cells of either line even when toxic concentratiions of caffein were used.
Abstract: The effect of UV irradiation was investigated on a standard line of HeLa cells and on a line sensitive to methyl methanesulphonate (MMS). The MMS-sensitive line was found to be more sensitive to UV irradiation than the parent line. When the two cell lines were plated in caffeine-containing medium immediately after UV irradiation, there was no reduction in the surviving fraction of cells of either line even when toxic concentratiions of caffein were used.
TL;DR: A critical test has shown that one important aspect of the exchange hypothesis is correct, namely that some aberrations that appear to be simple chromatid deletions are actually incomplete exchanges.
Abstract: The exchange hypothesis and the breakage-first hypothesis are the 2 major hypotheses that describe how chromosomal aberrations might be produced. A critical test has shown that one important aspect of the exchange hypothesis is correct, namely that some aberrations that appear to be simple chromatid deletions are actually incomplete exchanges. Furthermore, the relative frequency of those deletions that could be positively identified as incomplete exchanges was very close to that predicted from the exchange hypothesis. Because the sample was small and because a mixture of 2 deletion types (true, non-exchange, deletionsand incomplete exchanges between sister chromatids) could have given the same results, further experiments were performed. The results show that chromatid deletions are indeed of 2 types, since the relative proportion of exchange deletions is not the same in Chinese hamster cells as in rat kangaroo cells, nor is it the same in S and in G2 of Chinese hamster cells. Thus, some chromatid deletions are simple deletions arising from single lesions as expected on the basis of the breakage-first hypothesis and others are incomplete exchanges between sister chromatids as expected on the exchange hypothesis. It is clear, then, that neither hypothesis, as usually interpreted, is entirely correct nor incorrect, but rather that deletions are of 2 types according to mode of origin. Attempts to identify the 2 types morphologically have failed. The data also suggest that some of the chromosomal changes that we and others have considered to be gaps, are actually true deletions. This is important because many of the changes produced by chemicals in cultured mammalian cells are of this type.
TL;DR: It is suggested that the great difference in the spectrum of genetic damage observed in mammals relative to that reported for other organisms is due to differences in the repair system.
Abstract: Ethyl methanesulfonate (EMS) or methyl methanesulfonate (MMS) with a [ 14 C]alkyl label were injected intraperitoneally into (101 × C 3 H)F 1 hybrid male mice. Radiactivity levels were measured in various tissues and tissue fractions at eight time periods ranging from 15 min to 24 h after injection. Activity levels were also measured in the blood and urine, and respiration pattern analysis was carried out on exhaled 14 CO 2 . Distribution of these compounds is rapid, and approximately the injected dose w/w reaches the testis in an active form. However, EMS is rapidly hydrolyzed in vivo , and MMS is 4–6 times more effective in alkylating biological molecules. The amount of genetic damage done in the mouse (chromosome breakage) is correlated with in vivo alkylation of macromolecules. It is suggested that the great difference in the spectrum of genetic damage observed in mammals relative to that reported for other organisms is due to differences in the repair system.
TL;DR: Experimental evidence is presented that caffeine interferes strongly with the formation of enzyme-substrate (ES) complexes, presumably by binding to DNA at, or close to, the repairable photoproducts, which results in a lower equilibrium of complex formation in the dark.
Abstract: The rate of photoenzymatic repair (PER) obtained with continuous illumination of UV-irradiated E. coli Bs−1 cells is much decreased in the presence of 16 mg/ml caffeine. This inhibitory effect is usually not observed in B/r cells. It occurs in T1 phage infecting either Bs−1 or B/r, indicating that its absence in B/r cells has not a trivial explanation such as destruction or decreased uptake of the inhibitor. Experimental evidence is presented that caffeine interferes strongly with the formation of enzyme-substrate (ES) complexes, presumably by binding to DNA at, or close to, the repairable photoproducts. This results in a lower equilibrium of complex formation in the dark. A single caffeine molecule can block the formation of a complex; this effect is fully reversible when the caffeine is diluted out. Caffeine does not interfere with the photolysis of existing ES complexes. Failure to observe, under usual conditions, caffeine inhibition of PER in irradiated B/r cells is explained by the large number of UV lesions in these cells, compared to much smaller numbers in Bs−1 cells or in phage infecting either type of cell. Due to this high number, complex formation in B/r cells is so rapid that—in spite of the slowdown by caffeine—most of the PRE is tied up in ES complexes in the steady state during continuous illumination at moderate intensity. Only at very high light intensity, where the steady-state concentration of complexes is lower, is the caffeine inhibition observed. Correspondingly, illumination of irradiated Bs−1 cells at very low light intensity results in decreased caffeine inhibition of PER.
TL;DR: It was shown that the reduction in yield for chronic exposures was not the result of a depletion of oxygen during the 24-h irradiation, and it was suggested that the analysis of dose-response curves for exchange aberrations in terms of a dose-rate dependent 2-track process and adose-rate independent 1- track process might not be justified.
Abstract: Human peripheral blood lymphocytes were exposed, in vitro , to acute doses (2-min or 10-min exposures) of 250 kV X-rays and 60 Co γ-rays, or to chronic doses (24-, 48- or 72-h exposures) of γ-rays. Chromosome aberrations were scored at the first mitosis after stimulation with phytohemagglutinin. Yields of dicentric aberrations after X-irradiation agreed with those reported by Evans who obtained a dose exponent ( n ) of 1.17 ± 0.04 on a power law model. Our dose exponent for acute γ-irradiation was 1.24 ± 0.06 and the Relative Biological Effectiveness of 60 Co γ-rays compared with 250 kV X-rays was found to be 0.82 ± 0.03. The acute γ-ray data were analysed on a quadratic model on the assumption that the majority of dicentrics had been induced by a single ionizing track (the linear component) but that some were induced by two independent tracks (the quadratic component). On “classical” theory only the 2-track aberrations should be reduced by reducing the dose-rate (by increasing the exposure time) and the dose-response curve should become progressively more linear. In contrast we found that the dose-response curve for 24-h γ-exposures had a greater curvature ( n = 1.52 ± 0.10) than the acute response and the dicentric yields had fallen below the level of the I-track component of the acute curve. It was shown that the reduction in yield for chronic exposures was not the result of a depletion of oxygen during the 24-h irradiation. It is suggested that the analysis of dose-response curves for exchange aberrations in terms of a dose-rate dependent 2-track process and a dose-rate independent 1-track process might not be justified. However, further speculation on the present results must await resolution of the discrepancies between different laboratories in the shapes of dose-response curves for radiation-induced chromosome aberrations induced in peripheral blood lymphocytes in vitro
TL;DR: The extent of complexing of the repairable ultraviolet lesions in Haemophilus influenzae transforming DNA with yeast photoreactivating enzyme in the dark can be determined by applying intense light flashes, which cause repair of essentially all lesions complexed.
Abstract: The extent of complexing of the repairable ultraviolet lesions in Haemophilus influenzae transforming DNA with yeast photoreactivating enzyme in the dark can be determined by applying intense light flashes, which cause repair of essentially all lesions complexed. With full complexing of repairable lesions the kinetics of photoreactivation by steady illumination reflect only the photochemical reaction occurring in the enzyme-substrate complex. Complexes are heterogeneous with respect to their rates of photolysis, described by the first-order rate constant k 3 . At early stages of repair k 3 = k p I , where I is the light intensity and k p is the photolysis constant. The measured value of k p permits calculation of the product ϵΦ, where ϵ is the molar extinction coefficient for the complex, and Φ is the quantum yield for photolysis, giving an absolute action spectrum. In the region of most effective wavelengths (355–385 nm), ϵ > 10 4 liter·mole −1 ·cm −1 , and Φ > 0.1, with the possibility that Φ ∼ 1. k p is independent of temperature and ionic strength over a range producing large effects on the rate of complex formation, but does increase with pH over the range 6.7–7.4. For the slower repair of a minority of lesions the measured value of k p depends somewhat on intensity and continuity of illumination, suggesting some differences not yet understood. At the usual illumination intensities used for photoreactivation k 3 is greater than k 2 the rate constant for dark dissociation of complexes.
TL;DR: It seems probable that the initial dose-response curve has the expected square-law component but becomes destorted by secondary factors between irradiation and meiotic examination of cells.
Abstract: Translocation frequencies were studied in mouse spermatocytes derived from X-irradiated spermatogonia. Over the range from 50–800 R the dose-response relationship did not differ significantly from linearity, in agreement with previous findings of Leonard and Deknudt . It seems probable that the initial dose-response curve has the expected square-law component but becomes destorted by secondary factors between irradiation and meiotic examination of cells. Observed translocation frequencies were little affected by increasing length of time (from 11–30 weeks) between irradiation and examination, except for a possible decline at the highest dose (800 R). No significant frequency differences were found between mated and solitary males, or between those given whole-body or part-body (gonadal) irradiation.
TL;DR: The preliminary conclusion drawn from the experimental results is that segment extension is due to the inhibition of RNA and, concomitantly, protein synthesis or the failure of complex formation between DNA and specific proteins.
Abstract: When root tips of Vicia faba were treated with 5-azacytidine (5-ACR) or 5-azadeoxycytidine (5-ACD) local uncoiling (segment extension) of specific chromosome segments and chromatid aberrations was produced. The peak of cells with segment extension was observed 2–8 h after treatment (non-delayed effect); cells with chromatid aberrations appeared after recovery times of more than 20 h (delayed effect). Colchicine labelling of cells after 5-ACR treatment showed that chromatid aberrations were present in 4n cells, i.e. , they became induced during the interphase preceding the second mitosis. 5-ACR post-treatment after X-raying increased the frequency of X-ray-induced chromatid aberrations, and pretreatment was without influence on the aberration yield induced by X-rays alone. The preliminary conclusion drawn from the experimental results is that segment extension is due to the inhibition of RNA and, concomitantly, protein synthesis or the failure of complex formation between DNA and specific proteins. The incorporation of the analogues into DNA is presumed to be responsible for the induction of chromatid aberrations.
TL;DR: The lethal effects of X and UV radiations, N-methyl-N′-nitro-N-nitrosoguanidine and heat have been investigated in multinucleate spores from heterokaryotic mycelia of Phycomyces blakesleeanus, finding Functionally uninucleate cells, important in the isolation of recessive mutants, are obtained best with X-rays.
Abstract: The lethal effects of X and UV radiations, N-methyl-N′-nitro-N-nitrosoguanidine and heat have been investigated in multinucleate spores from heterokaryotic mycelia of Phycomyces blakesleeanus. According to their relation to the nuclei, 4 types of lethal events have been considered: mitotic (the affected nucleus cannot undergo unlimited mitoses); recessive (the affected nucleus can divide forever, but the cell dies if the affected nucleus is the only one able to divide forever); dominant (when a nucleus is affected, the cell dies irrespective of the condition of other nuclei); and cytoplasmic (the nuclei are not affected, but the cells dies). A theoretical prediction of the genetic changes produced by these events on the spore population has been compared to actual determinations of the proportions of heterokaryons among the survivors and the presence of recessive lethals in surviving heterokaryons. X-rays cause principally mitotic lethals, and, somewhat less frequently, recessive lethals. UV light produces mitotic and recessive lethals at similar rates; photoreactivation reverses them about equally and simulates a dose reduction. The lethal action of nitrosoguanidine depends on the pH and the chemical composition of the buffer; as extreme cases, in pH 7 citrate-phosphate buffer it consists mainly of equal proportions of mitotic and recessive events, but in pH 5 Tris-malate buffer cytoplasmic and recessive events seem predominant. Heat (55°) causes only, or nearly only, cytoplasmic lethality. Functionally uninucleate cells, important in the isolation of recessive mutants, are obtained best with X-rays. After treatments with UV radiation or nitrosoguanidine in pH 7 citrate-phosphate buffer leading to survival of one-tenth of the spores, about one-third of the survivors are functionally uninucleate.
TL;DR: Results indicate that a dose as low as 5 rad is mutagenic to mice, and fractionation or protraction of the dose reduced the effect.
Abstract: When a total dose of 300 rad X-rays was delivered to mouse spermatogonia in a single dose or in successive daily doses of 60 rad, 10 rad, or 5 rad the incidence of spermatocytes carrying translocations was 6.3, 3.4, 1.3, and 1.7% respectively i.e. fractionation or protraction of the dose reduced the effect. The possible explanations for this are being studied further. Providing one assumes that premutational damage does not persist for as long as 24 h, these results indicate that a dose as low as 5 rad is mutagenic to mice.
TL;DR: The mutator functions only in females, is partially dominant and appears to be incapable of reverting or mutating mutations it causes, conjectured in the light of current knowledge on the mechanism of action of bacterial and bacteriophage mutator genes.
Abstract: The genetic properties of an apparently new mutator gene in Drosophila melanogaster are described The mutator gene causes the recessive, sex-linked mutant gene, yellow -2 ( y 2 ), to revert to wild-type at an inordinately high rate (about 1 2500 y 2 genes) At a somewhat lower frequency it induces partial reversions of y 2 as well as mutations to a phenotypically more extreme allele The mutator is not locus-specific causing the recessive, sex-linked mutant forked -3 N to revert frequently to wild-type and white-apricot to mutate to a phenotypically white-eyed allele Linkage analysis has localized the mutator to map position 57 on chromosome 3 as a probable allele of c 3 G The mutator functions only in females, is partially dominant and appears to be incapable of reverting or mutating mutations it causes The possible mechanism of mutator action is conjectured in the light of current knowledge on the mechanism of action of bacterial and bacteriophage mutator genes
TL;DR: Starved, log-phase cells were more sensitive than stationary-phse cells to the single dose of ICR-70 employed, as evidenced by higher mutation frequencies and lower survival levels after treatment with the compound.
Abstract: The mutagenic activity of the acridine mustard, 2-methoxy-6-chloro-9[3- (ethyl-2-chloroethyl)aminopropylamino]acridine·2 (ICR-170), was tested in several strains of Saccharomyces cerevisiae. Starved, log-phase cells were more sensitive than stationary-phse cells to the single dose of ICR-70 employed, as evidenced by higher mutation frequencies and lower survival levels after treatment with the compound. This growth-phase effect could not be attributed to an unusually high frequency of mutations at a few sensitive loci.
A single strain of S. cerevisiae (S288C) was examined for the presence of the above described growth-phase effect using three other chemical mutagens: nitrous acid, s-propiolactone, and N-methyl-N′-nitrosoguanide (NG). With each mutagen, log- and stationary-phase cells responded differently, but none of these agents gave the extreme differences produced by ICR-170.
18 ICR-170-induced auxotrophs of strain S288C were tested for reversion with ICR-170 and NG. A majority (14 out of 18) of the mutants clearly reverted with ICR-170 and only slightly, or nota all all, with NG. One mutant reverted only with NG, and 3 reverted clearly with both NG and ICR-170.
TL;DR: Results indicate that UV-damaged DNA is transcribed and a protein important for the turnoff of respiration is formed.
Abstract: UV irradiation of Escherichia coli B/r cells causes a temporary inhibition of respiration. This inhibition begins about 60 min after irradiation. The duration of the inhibition depends, in part, upon the carbon source on which the cells were grown and its presence or absence at the time of irradiation. In cells grown on a mineral salts and glycerol medium, irradiation with 520 erg/mm 2 at 254 nm almost completely inhibits respiration for 4 h; the addition of exogenous amino acids to the growth medium favors early recovery of respiration. Experiments with caffeine show that excision of pyrimidine dimers is not necessary for the delayed inhibition of respiration, but is necessary for the subsequent recovery of respiration. If chloramphenicol, 5-fluorouracil, or an amber mutant of phage T4 is added to cells immediately after UV, the turnoff of respiration is prevented, but none of these agents reverses the inhibition once it has set in. These results indicate that UV-damaged DNA is transcribed and a protein important for the turnoff of respiration is formed.
TL;DR: Two commonly held explanations for mosaics induced by treating postmeiotic spermatozoa with chemical mutagens are incosistent with an analysis of the percent of mutant tissue produced in the F 1, and both of the initial models were rejected.
Abstract: This study shows that 2 commonly held explanations for mosaics induced by treating postmeiotic spermatozoa with chemical mutagens are incosistent with an analysis of the percent of mutant tissue produced in the F 1 . The first model tested assumes that mosaics are the results of altering one strand of the DNA double helix so that there will be an equal number of mutant and nonmutant nuclei following semiconservative replication. The second model assumes that alkylation of a base in DNA will cause a fixed probability of base pairing mistakes and may produced a mutation at any replication. In phage the probability of mispairing following alkylation is low so that a mutation likely occurs only once in 8 replications; therefore, most of the mutations are fixed after the first 2 divisions. If Drosophila is similar to phage, the mean frequency of mutant nuclei and the frequency distribution of mosaics by class of percent mutant tissue will be distinctly different for the 2 models. Males were fed ethyl methanesulfonate and mutations were detected in the F 1 by the specific locus method at the yellow ( y ) and white w loci. Agreement between this experiment and previous work with mosaics produced by chromosome aberrations was found in that the germ line developed from a small sample of poorly mixed nuclei that was independent of the phenotype of head and thorax. The latter finding allowed a selection of mosaics to be made independent of the germ line, and a method of analysis was developed for flies selected because they were mosaic in the head or thorax. Analyses of results from the eye mosaics in this experiment and from 3 experiments with the dumpy (dp) locus previously reported by others but not analyzed in this was were inconsistent with both original models. The average percent of mutant phenotype among the yellow mosaic observed in this experiment was also found inconsistent with both original models, and a frequency distribution of mosaics classified by percent of mutant tissue was inconsistent with both original models and a combination of the two; therefore, both of our initial models and a combination of the two were rejected. The data are consistent with delayed mutation in which an alkylated base has about a 50% probability of mispairing at each replication and producing a fixed mutation or with a multistranded model in which the postmeiotic eukaryote chromosome contains 2 parallel DNA molecules for each locus.
TL;DR: When mle mice were given single doses of X-rays and chromosomes at first meiotic metaphase were examined 8 or more weeks later, the incidences of cells with translocations after doses of 500, 600, 700 and 800 rad were 12.2, 14.2 and 6.8% resp.
Abstract: When mle mice were given single doses of X-rays and chromosomes at first meiotic metaphase were examined 8 or more weeks later, the incidences of cells with translocations after doses of 500, 600, 700 and 800 rad were 12.2, 14.0, 14.2 and 6.8% resp. This humped dose-response curve is in good agreement with other work.
TL;DR: In the irradiated males, the percentage of spermatocytes with chromosome rearrangements increased from 8.4 after 60 days to 12.6 after 100 days, and the yield of abnormal cells remained at that level from 100 days to 200 days and then decreased up to 450 days after irradiation.
Abstract: Male C57BL mice received local irradiation to the testes with an exposure of 600 R of X-rays. The irradiated mice were killed 60–600 days after treatment, the testes were removed and meiotic preparations made by an air-drying method. Most of the cells showed 20 bivalents (20II), but multivalent configurations were recorded in the spermatocytes from irradiated animals and from old control males. In the irradiated males, the percentage of spermatocytes with chromosome rearrangements increased from 8.4 after 60 days to 12.6 after 100 days. The yield of abnormal cells remained at that level from 100 days to 200 days and then decreased up to 450 days after irradiation. A small increase occurred after 500 and 600 days.