Showing papers on "Mutant published in 1968"
457 citations
TL;DR: The ability of the lac repressor to bind IPTG (isopropyl-l-thio-f-D-galactopyranoside) gives one a direct, quantitative measure of the number of molecules present, which suggests that there is about ten times more repressor in the ij strains.
Abstract: The gene that makes the lac repressor functions at an extremely low rate. It synthesizes only a few thousandths of a per cent of the total protein of an E. coli cell: about 5-10 molecules each generation.1 In order to study this molecule more easily, we have sought to enhance the amount present in a cell. Two approaches have been successful. The repressor gene, the i gene, itself can be mutated to a form that produces more repressor, or the number of copies of the gene can be drastically increased by incorporating the gene into a phage chromosome which will multiply in the cell. The combination of these two approaches yields a cell strain which can make 0.5 per cent of its protein lac repressor. The ij Mutant.-Several mutants that make about tenfold more repressor than the wild type have been found. These if mutants (q for quantity) were selected by forcing temperature-sensitive repressor mutants, strains constitutive at 430 and inducible at 300, to revert to an inducible phenotype at 430C. At the high temperature, the temperature-sensitive mutants make too little repressor, either because the protein itself is unstable (iTL) or because the final assembly of active repressor is blocked (iTSS).2 Although the reversion could simply correct the original defect, the temperature effects can also be overcome by producing more of the protein (or a more active protein: so that the small amount left at the high temperature will suffice). However, the ability of the lac repressor to bind IPTG (isopropyl-l-thio-f-D-galactopyranoside) gives one a direct, quantitative measure of the number of molecules present.1' By screening extracts from \"revertant\" strains, we could identify those mutants which, in contrast to the wild type, gave an easily detectable binding in the crude extract. The revertants were isolated using TONPG (o-nitrophenyl-1-thio-f3-D-galactopyranoside), which will inhibit the growth of lac constitutive cells that have a functioning lac permease. y(permease-) mutants will arise and can be coullterselected against by growth on lactose in the -presence of IPTG. Both iTSS and iTL strains have yielded overproducing derivatives. Table 1 shows the IPTG-binding data for some of these strains; the data suggest that there is about ten times more repressor in the ij strains. One of these mutants, a derivative of an iTSS strain, has been studied in detail, and was used to produce pure repressor for physical characterization (studies that will be reported elsewhere). The affinity of this ij repressor for IPTG has been checked and is the same as the wild type; therefore, the increase in the binding truly means an increase in amount of repressor. Dominance and Complementation.-To study further the properties of this i\" mutant, we constructed heterozygous diploids with a variety of i and o (operator)
348 citations
TL;DR: A genetic demonstration is presented that thymine starvation leads to the initiation of a new round of DNA replication, even if the chromosome is already being replicated at the time thymine is withheld.
288 citations
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: It is demonstrated that λ produces at least one component of the system responsible for general vegetative phage recombination, and that the bacterial recombination system can replace this phage function.
260 citations
TL;DR: Three λ dg phages carrying strong-polar mutations in the gal operon are denser than the corresponding phage carrying the wildtype gal operons or reversions of the mutations to the Gal+ phenotype.
Abstract: Three λ dg phages carrying strong-polar mutations in the gal operon are denser than the corresponding phages carrying the wildtype gal operon or reversions of the mutations to the Gal
+ phenotype. The latter phages have the same density. It is concluded that these strong-polar mutations are insertions of DNA into the gal operon. The amount of inserted DNA is different in the three mutations and is calculated to be 450, 1,080 and 1,800 nucleotide pairs respectively. The strong-polar phenotype is also found in a mutant supplied by A. Taylor which carries a Mu-1 phage integrated into the transferase gene.
217 citations
TL;DR: Results show the presence of a functional relation between the uvrB and uvrD genes and suggest that the UVRD gene participate in the repair synthesis at a step following that performed by the uVRB gene.
Abstract: SummaryTwenty-four UV sensitive strains which can not carry out the host cell reactivation and two which are deficient in recombination were isolated. By analyzing their properties and genetic locations, 21 UV sensitive strains were classified into the uvrA, B, and C groups and 3 strains into a group which has not been described. Two Rec- strains were classified in the recA group. The UV sensitive mutants of the new group are distinctly different from other mutants in their properties and in the sites of mutation. We named this group the uvrD.These uvrD mutants have the following properties. They have an intermediate sensitivity against UV irradiation and a higher sensitivity against γ-ray irradiation than those of other UV sensitive mutants. The UV damages which are repaired in the participation of the uvrD gene are photoreactivable. In the cells UV irradiated λ phage rapidly loses the susceptibility to photoreactivation during the incubation in broth with chloramphenicol. The DNA of the uvrD mutant is rapidly degraded at a small dose of UV light and to a large extent. The uvrD gene locates very close to the metE gene and uvrD- is dominant over uvrD+. The uvrD cells have the capacity to carry out UV reactivation for UV irradiated λ phage, in contrast to other UV sensitive mutants including the Rec- ones which turned out to have no capacity. A double mutant, uvrB uvrD, is about three times as sensitive as the uvrB mutant against UV irradiation and DNA degradation after UV irradiation takes place at much lower rate than the uvrD mutant. These results show the presence of a functional relation between the uvrB and uvrD genes and suggest that the uvrD gene participate in the repair synthesis at a step following that performed by the uvrB gene.
204 citations
TL;DR: Seven mutants of Haemophilus influenzae were isolated by the criterion of sensitivity to ultraviolet (UV) inactivation of colony formation and the influence of acriflavine on the survival of UV-irradiated transforming DNA with these strains as recipients showed some, but by no means complete, correlation from one type of sensitivity characterization to another.
Abstract: Seven mutants of Haemophilus influenzae were isolated by the criterion of sensitivity to ultraviolet (UV) inactivation of colony formation. These mutants and the wild type were characterized with regard to X-ray inactivation of colony formation, UV induction of division inhibition, the ability of the eight strains to act as recipients to UV-irradiated H. influenzae phage and transforming deoxyribonucleic acid (DNA), and the influence of acriflavine on the survival of UV-irradiated transforming DNA with these strains as recipients. The photoreactivable sector of transforming DNA with yeast photoreactivating enzyme was measured for the most UV-sensitive mutant and was found to be greater than that of wild type. Judged by the above criteria, the order of the strains' sensitivities shows some, but by no means complete, correlation from one type of sensitivity characterization to another, indicating that a minimum of two variables is needed to explain the differences in the strains. Acriflavine increases the UV sensitivity of transforming DNA except in the most sensitive mutant. This effect is usually, but not always, more pronounced in the case of the more UV-resistant marker. The acriflavine effect is postulated to be the result of at least two factors: (i) interference with repair of transforming DNA in the host cell, and (ii) interference with the probability of recombination between transforming DNA and host DNA.
199 citations
TL;DR: Two mechanisms must be involved in the synthesis of T4 late messenger: a competent form of DNA must be made available in the infected cell; and one or more “maturation” gene products must act on this competent DNA.
197 citations
TL;DR: A method has been developed to select for Escherichia coli mutants which lack certain nucleases, and mutants deficient in endonuclease I or RNase I were essentially identical to wild-type with respect to their general biological properties.
193 citations
TL;DR: The bacterial recA gene participates in the induction by UV irradiation of the clear mutation of phage λ and the Lac- mutation of bacteria as mentioned in this paper, and acts upon DNA irradiated with UV light.
Abstract: The bacterial recA gene participates in the induction by UV irradiation of the clear mutation of phage λ and the Lac- mutation of bacteria. The necessary function is induced by irradiation of Rec+ bacteria and acts upon DNA irradiated with UV light.
TL;DR: Proteins made by E. coli cells infected with bacteriophage T4 were analyzed by a method which combined disc electrophoresis and autoradiography, showing that the early proteins are not controlled as a single homogeneous class all members of which are synthesized during the same time periods.
TL;DR: It is concluded that the mitochondrial ATPase itself is not altered in the "petite" mutant, and the unusual properties of the enzyme associated with the mutant mitochondria reflect an impairment of its linkage to the inner mitochondrial membrane.
TL;DR: A benzidine-H2O2 staining procedure and genetic tests were used for the detection of cytochrome c-deficient mutants of the cy1, cy2, cy3, cy4, and cy6 loci and it was revealed that all of the revertants from eight of the Cy1 mutants apparently contained normal iso-1-cy tochrome c, while a revertant which contained an altered protein was obtained from each of the other seven cy1 mutants.
TL;DR: Evidence is presented that the degradation of newly synthesized T4 DNA which occurs in infected cells lacking the phage-directed dCTPase occurs in two similar stages; in such cells cytosine is substituted extensively for the hydroxymethylcytosine normally found in T4 phage DNA.
TL;DR: Host DNA synthesis does not stop when chloramphenicol is present before and during the infection, which indicates that a phage-specific protein is responsible for the cessation of host DNA synthesis.
TL;DR: In Bacillus subtilis a series of four enzymes is responsible for the degradation of l-histidine to ammonia, formamide, and l-glutamic acid, and two mutants can be found in which the three enzymes are constitutive but still subject to catabolite repression.
TL;DR: A selection procedure was developed for the isolation of mutants of Escherichia coli which require lipoic acid, acetate+succinate, or lysine + methionine for aerobic growth with glucose and indicated that the genetic loci of some 36 independently isolated lip - mutants are confined to a small segment of the E. coli chromosome between the purE and suc sites.
Abstract: SUMMARY: A selection procedure was developed for the isolation of mutants of Escherichia coli which require lipoic acid, acetate+succinate, or lysine + methionine for aerobic growth with glucose. The properties of the mutants requiring lipoic acid (lip
-) were compared with those of suc
- mutants which lack α-ketoglutarate dehydrogenase and require succinate or lysine + methionine. Genetic analysis by conjugation with Hfr and F’ donors indicated that the genetic loci of some 36 independently isolated lip
- mutants are confined to a small segment of the E. coli chromosome between the purE and suc sites. By using phage P1 no cotransduction of lip with suc, glt A or purE could be demonstrated, but suc, gltA and gal were cotransducible and the relative order of these sites was determined.
TL;DR: It is suggested that genes 4, 26, 28, 31, 38, 50, 51, and 65 are the most likely to code for gene products which function catalytically (if, in fact, any such functions exist).
TL;DR: Certain temperature-sensitive (ts(-)) mutants of yeast which cannot be corrected by nutritional supplementation exhibited a rapid cessation of protein synthesis after a shift to the restrictive temperature, and genetic and biochemical tests permitted a division of these mutants into four classes.
Abstract: Certain temperature-sensitive (ts−) mutants of yeast which cannot be corrected by nutritional supplementation exhibited a rapid cessation of protein synthesis after a shift to the restrictive temperature. Genetic and biochemical tests permitted a division of these mutants into four classes. This division was based upon genetic complementation patterns among the mutants and an investigation of glucose incorporation into macromolecules and polyribosome content in the mutants after a shift to the restrictive temperature. A study of these parameters in the parent strain (ts+) in the presence of certain well-characterized inhibitors allowed a tentative identification of the biochemical defects in each of the four classes. The properties of the mutants in class IA were consistent with the hypothesis that they result from a defect in the initiation of polypeptide chains or in ribonucleic acid synthesis; mutants in class IB from a defect in the elongation of polypeptide chains; mutants in class IIA from a defect in energy metabolism; and mutants in class IIB from a lesion affecting membrane function.
TL;DR: Chromatography of total DNA from both wild-type cells and the cytoplasmic petite mutant has revealed the presence of a small nucleic acid component which is extremely rich in guanine; its origin is still unknown.
TL;DR: Analysis of vegetative and sexual progeny of isolated zygotes from a number of crosses between resistant and sensitive strains indicated that different mitochondrial types, both sensitive and resistant, co-exist in the yeast cell and are distributed at random among daughter cells under non-selective conditions.
Abstract: Erythromycin-resistant mutants were separated into two categories showing Mendelian and non-Mendelian inheritance of resistance respectively. The cytoplasmic factor was located in the mitochondrion based on the fact that the loss of the mitochondrial genetic unit associated with the petite mutation (the ρ factor, assumed to be the mitochondrial DNA) resulted in a corresponding permanent loss of resistance. Conversely, the petite mutation in gene resistant mutants had no effect on the inheritance of resistance.Analysis of vegetative and sexual progeny of isolated zygotes from a number of crosses between resistant and sensitive strains indicated that different mitochondrial types, both sensitive and resistant, co-exist in the yeast cell and are distributed at random among daughter cells under non-selective conditions. Only resistant mitochondria are in evidence if zygotes are put down to proliferate on medium containing the antibiotic.Resistant strains were tested for retention of resistance following anaerobic culture (known to cause disruption of mitochondria). The cytoplasmic mutants retained their resistance but two gene-resistant mutants tested both lost their resistance. It was suggested in the latter case that resistance is dependent on the existence of intact mitochondrial membrane (possibly inner membrane). In the former mutants the mechanism of resistance may be the alteration of one or other of the components of the protein-synthesizing system of the organelle.
TL;DR: Certain genetic sequences were proved by three-factor crosses involving a mutant adapted to guanidine resistance showing that recombination frequencies were additive, and an additive linear genetic map comprising one linkage group was obtained.
TL;DR: During the course of preliminary investigations into the biochemical basis of dor female-sterility, an attempt was made to prevent the accumulation of isoxanthopterin in mutant females by genetic means, resulting in the discovery of a highly specific synthetic lethal system involving dor and a non-allelic third chromosome mutant, rosy (ry) .
Abstract: sex-linked mutant deep orange (dor) of Drosophila melanogaster is Tzonsible for a peculiar type of female sterility: mutant females produce no progeny when crossed to mutant males but yield some offspring (heterozygous daughters) when mated to wild-type males (MERRELL 1947). The effects of this mutant on embryonic development have been extensively studied by COUNCE (1956a) and more recently by HILDRETH and LUCCHESI (1967). In addition to the sterility phene, dor alters the pigmentation of the eyes (which are orange in color) and confers an abnormal spectrum of relative pteridine concentrations. An unusual characteristic of dor is that isoxanthopterin appears to be accumulated by mutant females (COUNCE 1957). During the course of preliminary investigations into the biochemical basis of dor female-sterility, art attempt was made to prevent the accumulation of isoxanthopterin in mutant females by genetic means. This resulted in the discovery of a highly specific synthetic lethal system involving dor and a non-allelic third chromosome mutant, rosy (ry) . The dor-ry system is similar to three other synthetic lethal systems, previously described in D. melanogaster: purpleoid (pd) and Purpleoider (Pdr) (BRIDGES 1922; as cited in BRIDGES and BREHME 1944) ; prune (pn) and Prune-killer (K-pn) ( STURTEVANT 1956) ; and Henna-recessiue-3 (Hnr3) and rosy (ry6) (TAIRA 1960; GOLDBERG, SCHALET and CHOVNICK 1962). A search was undertaken for the purpose of uncovering additional interactions among some of the mutants mentioned above. Since six of the latter affect eye color and/or pteridine levels, a number of other eye color mutants were tested. In addition, the female sterile mutant fused (fu) , similar in many respects to dor (although allowing lethal embryos to develop further than dor embryos (COUNCE 195613) ). was used in
TL;DR: Five mutants of bacteriophage λ defective in vegetative genetic recombination have been isolated and characterized for some of their genetic and physiological properties, and all five mutations probably affect a single gene, which is designated red.
TL;DR: It is established that erythromycin resistance is inherited extrachromosomally and it is shown that the cytoplasmic determinant for erydynamic resistance and the factor associated with the cytopsized petite mutation, while closely related, do not appear to be identical.
Abstract: control of the formation of mitochondria. From these studies it has been recognized that cytoplasmic genetic determinants as well as chromosomal genes are involved in the biogenesis of yeast mitochondria., 2 Following the recognition of the occurrence of mitochondrial DNA,3 4 attention has recently been focused on the relationship between mitochondrial DNA and the cytoplasmic determinant.5 However, the information on this latter subject is limited and is derived from the study of a single class of mutant of this determinant, the respiratory-deficient cytoplasmic petite. This irreversible mutation is phenotypically characterized by the inability of the cell to form a number of components of the respiratory system, including cytochromes a, a3, b, and ci.6 A clearer understanding of the role of cytoplasmic determinants in mitochondrial biogenesis could result from the characterization of new types of cytoplasmic mutations which do not result in such extensive biochemical changes. This would thus simplify the biochemical analyses as well as providing additional cytoplasmic markers to assist further genetic studies. We have reported that the antibiotics chloramphenicol, lincomycin, and the macrolides erythromycin, carbomycin, spiramycin, and oleandomycin selectively inhibit in vitro amino acid incorporation by yeast mitochondria, while not affecting the yeast cytoplasmic ribosomal system.7' 8 Further, these antibiotics do not affect the growth of S. cerevisiae on fermentable substrates but reversibly inhibit the in vivo synthesis of cytochromes a, a3, b, and cl; the inhibited cells appear to be phenocopies of the cytoplasmic petite mutant.9, 10 This laboratory has also described the isolation of yeast mutants with varying degrees of sensitivity to the aforementioned antibiotics.1l The mutants selected for resistance to high levels of erythromycin have been shown to contain mitochondria having an amino acid-incorporating activity which is completely resistant to the drug.l2 It was also shown that the inheritance of resistance to erythromycin did not segregate as a single chromosomal gene.7 This paper establishes that erythromycin resistance is inherited extrachromosomally. In addition, it is shown that the cytoplasmic determinant for erythromycin resistance and the factor associated with the cytoplasmic petite mutation, while closely related, do not appear to be identical. Materials and Methods.-Nomenclature: The following symbols have been adopted to represent the various mutants used in this paper. The symbol p (rho) represents the cytoplasmic factor as described by Sherman,2 where p+ and p designate the ability or inability, respectively, to synthesize the respiratory enzymes cytochromes a, a3, b, and cl. 903
TL;DR: Thiaisoleucine-resistant mutants of Escherichia coli strain K-12 which exhibited reduced isoleucyl soluble ribonucleic acid synthetase activity were isolated and grew more slowly than wild type and were derepressed for three of the five enzymes in the pathways to isoleukine and valine.
Abstract: Thiaisoleucine-resistant mutants of Escherichia coli strain K-12 which exhibited reduced isoleucyl soluble ribonucleic acid synthetase activity were isolated. Resistance was apparently achieved by the selection of a synthetase with a 10-fold decrease in apparent affinity for thiaisoleucine. This mutation also resulted in a 2.5-fold decrease in apparent affinity for the natural substrate, l-isoleucine, and less activity than found in wild type. The mutants grew more slowly than wild type and were derepressed for three of the five enzymes in the pathways to isoleucine and valine.
TL;DR: The selfsterility of the para-aminobenzoic acid-requiring mutant appears to be pleiotropically related to the auxotrophic condition, since self-sterility does not segregate from nutritional dependence in progeny of crosses.
Abstract: A B S T R A a T Physcomitrella patens is a monoecious, cleistocarpous moss which completes its life cycle under defined conditions in 7 to 8 weeks. Sexual reproduction is readily obtained by culturing gametophytes at la to 19 C. AMutants were induced by treatment of either spores or protonemal cells with ethyl methane sulfonate, N-methyl-N'-nitro-N-nitrosoguanidine and X-rays. Thiamine, para-aminobenzoic acid, niacin and yeast extract auxotrophs were obtained. Growth response to various supplements was studied in the auxotrophic mutants. Five yellow mutants and two morphological mutants were induced. The chlorophyll content of the yellow mutants is reduced 35-65% of wild type. The self-sterile, para-aminobenzoic acid-dependent mutant was used as the archegonial parent in crosses with a yellow mutant and a morphological mutant. The selfsterility of the para-aminobenzoic acid-requiring mutant appears to be pleiotropically related to the auxotrophic condition, since self-sterility does not segregate from nutritional dependence in progeny of crosses. On the basis of tests with heterozygous diploids obtained by aposporous regeneration of capsule cells, two mutant alleles were shown to be recessive to their respective wild
TL;DR: It is suggested that cys -3 is a regulatory gene which exerts positive control over enzyme synthesis and is not a large deletion, a super-repressor mutation, or an extreme polar mutant.
TL;DR: The present report describes a procedure for the isolation of bacterial mutants with tcmperaturesensitive synthesis of DNA and the characterization of two mutants representative of the types which were most frequently encountered.
Abstract: DESPITE considerable interest in recent years, the replication of bacterial DNA and the mechanism of its regulation are still poorly understood, as can be seen in recent reviews of the subject (LARK 1966; MAALBE and KJELDGAARD 1966). One approach to the study of essential cellular syntheses is through the study of temperature-sensitive mutants (APIRION 1966; EPSTEIN et al., 1963; NEIDHARDT 1966). Already several papers have appeared describing bacterial mutants impaired in synthesis of DNA at higher temperature ( BONHOEFFER 1966; KOHIYAMA et al. 1966; MENDELSON and GROSS 1967). The present report describes a procedure for the isolation of bacterial mutants with tcmperaturesensitive synthesis of DNA and the characterization of two mutants representative of the types which were most frequently encountered. The mutants studied resemble the two classes found previously (KOHIYAMA et al. 1966); but from the experiments presented here, it is evident that at least one of them represents a new kind of block in DNA synthesis. A preliminary report of these mutants has been presented ( FANGMAN 1966).