Showing papers on "Mutant published in 1974"
TL;DR: Preliminary results from mutant strains of Pseudomonas putida mt-2 and from a mutant defective in the regulation of the plasmid-carried pathway suggest that the wild type contains two benzoate oxidase systems, one on thePlasmid which is nonspecific in both its catalysis and its induction and one in the chromosome which is more specific to benzoates as substrate and is specifically induced by benzosate.
Abstract: Mutant strains of Pseudomonas putida (arvilla) mt-2 which have lost the ability to grow at the expense of m- or p-toluate (methylbenzoate) but retain the ability to grow with benzoate arise spontaneously during growth on benzoate; this genetic loss occurs to a lesser extent during growth on nonaromatic carbon sources in the presence of mitomycin C. The mutants have totally lost the activity of the enzymes of the divergent meta pathway with the possible exception of 2-oxopent-4-enoate hydratase and 4-hydroxy-2-oxovalerate aldolase; unlike the wild type they utilize benzoate by the ortho pathway. Evidence is presented that these mutants have lost a plasmid coding for the enzymes of the meta pathway, which may be transmitted back to them or into other P. putida strains. Preliminary results from these mutants and from a mutant defective in the regulation of the plasmid-carried pathway suggest that the wild type contains two benzoate oxidase systems, one on the plasmid which is nonspecific in both its catalysis and its induction and one on the chromosome which is more specific to benzoate as substrate and is specifically induced by benzoate.
483 citations
TL;DR: Examination of the survival responses of multiple-mutant strains indicated a minimum of two pathways in the repair of X-ray damage, and a number of the mutants have been mapped and these were found to be dispersed over the genome.
Abstract: A set of 64 mutants of Saccharomyces cerevisiae that confer sensitivity to X-ray inactivation were analyzed genetically to determine the number of genetic loci involved. The mode of interaction of various combinations of mutants was also determined. A minimum of 17 genes, when mutant, increase X-ray sensitivity of yeast, primarily by eliminating the resistance of budding haploid cells and by removing the shoulder on the survival curves of diploid cells. Eight mutant loci affect principally X-ray sensitivity while the remaining genes also control sensitivity to ultraviolet. Some of the genes when homozygous block sporulation or result in partial or complete sterility. Examination of the survival responses of multiple-mutant strains indicated a minimum of two pathways in the repair of X-ray damage. A number of the mutants have been mapped and these were found to be dispersed over the genome.
469 citations
TL;DR: Five Pillars of Evolution were culled from the accumulated evidence on molecular evolution and theoretical considerations of the population dynamics of mutant substitutions.
Abstract: The following five principles were deduced from the accumulated evidence on molecular evolution and theoretical considerations of the population dynamics of mutant substitutions: (i) for each protein, the rate of evolution in terms of amino acid substitutions is approximately constant/site per year for various lines, as long as the function and tertiary structure of the molecule remain essentially unaltered (ii) Functionally less important molecules or parts of a molecule evolve (in terms of mutant substitutions) faster than more important ones (iii) Those mutant substitutions that disrupt less the existing structure and function of a molecule (conservative substitutions) occur more frequently in evolution than more disruptive ones (iv) Gene duplication must always precede the emergence of a gene having a new function (v) Selective elimination of definitely deleterious mutants and random fixation of selectively neutral or very slightly deleterious mutants occur far more frequently in evolution than positive Darwinian selection of definitely advantageous mutants
467 citations
TL;DR: The selection of auxotrophic mutants of Chinese Hamster Ovary cells and the genetic and biochemical characterization of two mutant lines are described and it is suggested that a possible function of polyglutamyl residues is to aid cellular retention of folates.
252 citations
TL;DR: This chapter reviews gene or point mutations and discusses the fine structure of mutation-induced point mutations in mice and finds that with postnatal irradiation at any age, the progeny will be derived from irradiated dictyate oocytes, unless fertilization of the eggs takes place within 12 hours of the irradiation.
Abstract: Publisher Summary This chapter reviews gene or point mutations. It also discusses the fine structure of mutation-induced point mutations in mice. The work on mutation induction in mice has lead to an accurate assessment of human genetic hazards from radiation. Induced point mutations are detected and studied mainly by genetic methods, although biochemical techniques have also been used. Male germ cells take up a more central or medullary position whereas female germ cells take up a more peripheral or cortical one. It has been found that on the development and radiation response of germ cells in female mice that with postnatal irradiation at any age, the progeny will be derived from irradiated dictyate oocytes, unless fertilization of the eggs takes place within 12 hours of the irradiation. With neonatal and late fetal irradiation, exposed germ cells are normally in predictyate stages of meiotic prophase. Irradiations of younger embryos expose oogonia and their precursors. The specific locus method is the most efficient way of studying point mutations in mice. It is designed to detect mutations affecting a particular set of loci in the mouse that are chosen because their known mutant alleles have a clear-cut and easily visible effect.
233 citations
TL;DR: It is concluded that in zygotic meiosis the premeiotic DNA synthesis is confined to zygotes after conjugation has been completed, as synchronized mitotic division was observed in all the strains as a first response to the shift.
232 citations
TL;DR: A series of isonuclear cytoplasmic petite (ϱ−) mutants presenting various patterns of large deletions and retentions in the C321R — E514R region was used to study the functional organization of mitochondrial DNA.
225 citations
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TL;DR: A misuse of the term suppressor which originated as a designation for those mutations occurring in some other gene, the suppressor gene, and which now must be defined as an external suppressor.
Abstract: Suppressors are genes which suppress the expression of mutant phenotypes. The suppressors can be considered to be mutant genes themselves since they are generally not found in the wild type strains but are obtained by selecting for revertants of the mutant phenotype. A revertant arising by a mutation other than a base change in the original mutant codon carries a suppressor. If the new event occurred at another site within the original mutant gene, it is called by some an intra-locus suppressor. However, in our view this is a misuse of the term suppressor which originated as a designation for those mutations occurring in some other gene, the suppressor gene, and which now must be defined as an external suppressor. The external or extra-locus suppressors can be further classified as being either functional suppressors or informational suppressors.
219 citations
TL;DR: A function of dam -specified 6-methyl adenine residues in DNA would, therefore, appear to be the protection of DNA from a nuclease(s) that causes the development of breaks.
216 citations
TL;DR: A set of non-complementing, closely linked, ethyl methanesulphonate-induced mutations in Caenorhabditis elegans specifically affects the structure and function of body-wall muscle cells but not the pharyngeal musculature.
208 citations
TL;DR: A mutator gene, mutD5, whose phenotype is conditional, has been identified in Escherichia coli and by P1 transduction it has been shown to lie at about 5.7 min on the chromosome, being co-transduced with proA and argF.
Abstract: A mutator gene, mutD5, whose phenotype is conditional, has been identified in Escherichia coli By P1 transduction it has been shown to lie at about 57 min on the chromosome, being co-transduced with proA and argF In rich medium, streptomycin- and nalidixic acid-resistant mutation frequencies are 50 to 100 times higher than those in minimal medium In minimal medium, the mutD5-induced mutation frequencies are still 50 to 100 times above co-isogenic wild-type (mut+) levels Similar results were obtained with all markers tested Mutant frequencies can be raised by thymidine in the medium at concentrations as low as 004 μM, or by the endogenous generation of thymidine from thymine plus a deoxyribosyl donor Deoxyadenosine, various ribonucleosides, thymine, and 2-deoxyribose do not stimulate mutation None of these effects are related to growth rate, since growth rate and mutation rate can be decoupled completely
TL;DR: The ICR compounds, noncarcinogenic intercalating agents, show a broader specificity of mutagenesis, and the alkylating carcinogen N-methyl-N'-nitro-N-nitrosoguanidine appears to have a similar dual specificity.
Abstract: Other investigators have shown that several polycyclic carcinogens are frameshift mutagens in Salmonella. Mutagenic potency of these compounds is assessed by ability to induce reversion of histidine-requiring frameshift mutants to prototrophy. One frameshift mutation in the histidinol dehydrogenase gene, hisD3052, is unusually sensitive to mutagenesis by certain polycyclic carcinogens. We find that the 3052 mutation is a - 1 deletion, probably loss of a G.C pair from a DNA repeat of [unk]. The polycyclic carcinogens tested (e.g., 2-nitroso-fluorene) revert 3052 by deleting a [unk] doublet from the DNA sequence [unk], which is close to the 3052 site. This rare mispairing-prone sequence represents the carcinogen-sensitive "hotspot" in 3052. The ICR compounds, noncarcinogenic intercalating agents, show a broader specificity of mutagenesis. Reversion with these mutagens occurs predominantly by two mechanisms: one identical to that of the polycyclic carcinogens, and the other by +1 additions in a third DNA tract narrowly separated from the 3052 site. The alkylating carcinogen N-methyl-N'-nitro-N-nitrosoguanidine appears to have a similar dual specificity. DNA base changes in 3052 revertants have been correlated with properties of histidinol dehydrogenase in crude extracts. This correlation of DNA base sequence with electrophoretic and other properties of the mutant proteins allows one to analyze easily the specificity of new mutagens that mutate this strain.
TL;DR: This work isolated and characterized a series of mutants (cfs) that restored flagella-forming ability in a Crp strain of E. coli and proposed a regulatory function for the product of the flaI gene, which is suggested to be the step in flagellar synthesis that is catabolite sensitive and requires cAMP.
Abstract: In Escherichia coli, the synthesis of the flagellar organelle is sensitive to catabolite repression. Synthesis requires the presence of the cyclic adenosine monophosphate receptor protein (Crp) and 3′,5′-cyclic adenosine monophosphate (cAMP); i.e., mutants that lack Crp or adenylcyclase (Cya) synthesize no flagella. We isolated and characterized a series of mutants (cfs) that restored flagella-forming ability in a Crp strain of E. coli. The mutations in these strains were transferred onto episomes and they were then introduced into a variety of other strains. The presence of the mutation resulted in flagella synthesis in Cya and Crp strains as well as in the wild type grown under conditions of catabolite repression. Deletion analysis and other genetic studies indicated that: (i) the cfs mutations had a dominant effect when they were in the transconfiguration in merodiploids: (ii) they occurred in or very close to the flaI gene: and (iii) their expression required the presence of an intact flaI gene adjacent to the cfs mutation. Biochemical studies showed that the synthesis of at least two flagellar polypeptides, the hook subunit and an amber fragment of flagellin, were absent in strains that carried a cya mutation. Their synthesis was depressed in strains grown under conditions of catabolite repression. The presence of the cfs mutation restored the specific synthesis of these two polypeptides. We suggest that the formation of the flaI gene product is the step in flagellar synthesis that is catabolite sensitive and requires cAMP. We propose a regulatory function for the product of the flaI gene.
TL;DR: It is probable that the chemical basis of resistance is the elimination of ethidium binding sites due to the specific alterations in the nucleotide sequence, since the mutant RNA was found to bind less ethidium than the wild-type molecules.
TL;DR: It is suggested that the predominant means for abolishing iso-1-cytochrome c by mutations are either through a complete loss, such as produced by chain terminating codons, or impairments through drastic changes of tertiary structure which lead to instability and thermolability.
Abstract: A medium containing chlorolactate has been devised to enrich for mutants that are unable to utilize lactate for growth, and therefore that may be defective in cytochrome c. Complementation tests of 6,520 chlorolactate-resistant mutants that were obtained spontaneously or induced with UV, ICR-170, or nitrosoimidazolidone resulted in the identification of 195 mutations at the cyc1 locus, which controls the primary structure of iso-1-cytochrome c. These 195 mutants, with 16 cyc1 mutants previously isolated, were examined for total cytochrome c by spectroscopic methods, growth on lactate medium, suppressibility by defined nonsense suppressors, mutational sites by x-ray-induced recombination, ability to revert, and in 86 cases, whether intragenic revertants contain altered iso-1-cytochrome c. Except for the deletion mutant cyc1-1, all of the mutants appeared to contain single-site mutations that could be assigned to at least 35 different sites within the gene. The cyc1 mutants either completely lacked iso-1-cytochrome c or contained iso-1- cytochromes c that were completely or partially nonfunctional. In spite of the fact that the cyc1 mutants obtained by the chlorolactate procedure were selected on the basis of defective function, 68% appeared to completely lack iso-1-cytochrome c. The remaining cyc1 mutants contained below normal amounts of iso-1-cytochromes c. Studies at several incubation temperatures indicated that these nonfunctional iso-1-cytochromes c were thermolabile. It is suggested that the predominant means for abolishing iso-1-cytochrome c by mutations are either through a complete loss, such as produced by chain terminating codons, or impairments through drastic changes of tertiary structure which lead to instability and thermolability.
TL;DR: It is suggested that the activity of the spo T gene product is regulated by some consequence of downshift, and plays a role in the phosphorylation of ppGpp to pppGpp preparatory to further metabolism.
TL;DR: It is concluded that yeast requires a functional repair system for mutation induction by chemical agents.
Abstract: Two genes, rad6 and rad9 , that confer radiation sensitivity in the yeast Saccharomyces cerevisiae also greatly reduce the frequency of chemically-induced reversions of a tester mutant cyc1-131 , which is a chain initiation mutant in the structural gene determining iso-1-cytochrome c . Mutations induced by ethyl methanesulfonate (EMS), diethyl sulfate (DES), methyl methanesulfonate (MMS), dimethyl sulfate (DMS), nitroquinoline oxide (NQO), nitrosoguanidine (NTG), nitrogen mustard (HN2), β-propiolactone, and tritiated uridine, as well as mutations induced by ultraviolet light (UV) and ionizing radiation were greatly diminished in strains homozygous for either the rad6 or rad9 gene. Nitrous acid and nitrosoimidazolidone (NIL), on the other hand, were highly mutagenic in these repair-deficient mutants, and at low doses, these mutagens acted with about the same efficiency as in the normal RAD strain. At high doses of either nitrous acid or NIL, however, reversion frequencies were significantly reduced in the two rad mutants compared to normal strains. Although both rad mutants are immutable to about the same extent, the rad9 strains tend to be less sensitive to the lethal effect of chemical mutagens than rad6 strains. It is concluded that yeast requires a functional repair system for mutation induction by chemical agents.
TL;DR: Evidence is presented that a particular gene may regulate lattice assembly in the body wall muscle cells of the nematode Caenorhabditis elegans, and a temperature-sensitive mutation can prevent the appearance of normal myofilament lattices in this muscle.
Abstract: THE assembly of contractile and calcium-related regulatory proteins into functioning myofilament arrays within muscle cells and the genetic control of muscle differentiation are still largely unknown processes1–2. Here we present evidence that a particular gene may regulate such lattice assembly in the body wall muscle cells of the nematode Caenorhabditis elegans. A temperature-sensitive mutation in this gene can prevent the appearance of normal myofilament lattices in this muscle without affecting the amounts of major contractile proteins present. The organised or defective adult structures once formed in mutant muscle are stable to changes in temperature.
TL;DR: The isolation of a strain K mutant is described, which is resistant to both phages and yet bears many pili serologically similar to those of its parent.
TL;DR: The genetic mapping of a locus of the Escherichia coli chromosome involved in the expression of the N gene function of phage λ suggests that the nus + allele is responsible for theexpression of a function necessary for N product activity.
TL;DR: It is concluded that the mutants isolated from Escherichia coli K-12 have some defect in cell division after low doses of UV irradiation, similar to the lon(-) or fil(+) mutant of E. coli.
Abstract: Two ultraviolet light (UV)-sensitive mutants have been isolated from Escherichia coli K-12. These mutants, designated RuvA(-) and RuvB(-), were controlled by a gene located close to the his gene on the chromosome map. They were sensitive to UV (10- to 20-fold increase) and slightly sensitive to gamma rays (3-fold increase). Host cell reactivation, UV reactivation and genetic recombination were normal in these mutants. Irradiation of the mutants with UV resulted in the production of single-strand breaks in deoxyribonucleic acid, which was repaired upon incubation in a growth medium. After UV irradiation, these mutants resumed deoxyribonucleic acid synthesis at a normal rate, as did the parent wild-type bacteria, and formed nonseptate, multinucleate filaments. From these results we concluded that the mutants have some defect in cell division after low doses of UV irradiation, similar to the lon(-) or fil(+) mutant of E. coli. The ruv locus was divided further into ruvA and ruvB with respect to nalidixic acid sensitivity and the effect of minimal agar or pantoyl lactone on survival of the UV-irradiated cell. The ruvB(-)mutant was more sensitive to nalidixic acid than were ruvA(-) and the parent strain. There was a great increase in the surviving fraction of the UV-irradiated ruvB(-) mutant when it was plated on minimal agar or L agar containing pantoyl lactone. No such increase in survival was observed in the ruvA(-) mutant.
TL;DR: Five temperature-sensitive mutants of simian virus 40 (SV40), isolated and characterized by Tegtmeyer and Ozer (1971) , have been mapped by marker rescue using endo R fragments of wild-type SV40 DNA.
TL;DR: D mutants continue viral DNA replication at the restrictive temperature after preincubation at the permissive temperature and the viral DNA synthesized in D mutants under these conditions progresses in normal fashion through replicative intermediate molecules to mature component I and II DNA molecules.
Abstract: Temperature-sensitive mutants of simian virus 40 (SV40) have been classified as those that are blocked prior to viral DNA synthesis at the restrictive temperature, "early" mutants, and those harboring a defect later in the replication cycle, "late" mutants. Mutants of the A and D complementation groups are early, those of the B, C, and BC groups are late. Our results confirm earlier reports that A mutants are defective in a function required for the initiation of each round of viral DNA synthesis. D mutants, on the other hand, continue viral DNA replication at the restrictive temperature after preincubation at the permissive temperature. The length of time required for D function to be expressed at the permissive temperature-after which infection proceeds unabated on shifting of the cultures to the restrictive temperature-is 10 to 20 h. The viral DNA synthesized in D mutants under these conditions progresses in normal fashion through replicative intermediate molecules to mature component I and II DNA molecules.
TL;DR: At least two endonucleolytic activities that preferentially incise ultraviolet (UV)-irradiated DNA exist in extracts of E. coli and one of these activities elutes from phosphocellulose with 0.25 M potassium phosphate, pH 7.5.
Abstract: At least two endonucleolytic activities that preferentially incise ultraviolet (UV)-irradiated DNA exist in extracts of E. coli. These two activities can be separated by phosphocellulose chromatographic fractionation. The subject of this paper is one of these activities, which elutes from phosphocellulose with 0.25 M potassium phosphate, pH 7.5. This endonucleolytic activity specific for UV-irradiated DNA is absent from partially purified extracts of uvrA and uvrB mutants, which are defective in excision of pyrimidine dimers, but is present in normal amounts in the uvrC excision-defective mutant. The enzyme binds very tightly and specifically to UV-irradiated DNA. Binding can be prevented by prior treatment of the irradiated DNA with photoreactivating enzyme. This binding activity is absent in uvrA and uvrB mutants, but present in uvrC and uvrD mutants.
TL;DR: It is shown that phage P1 cotransduces the genetic locus conferring this property and the genes for the utilization of l-fucose and an enzyme catalyzing formation of a reduced fermentation product anaerobically in wild-type cells functions aerobically to oxidize this same product in the mutant.
Abstract: A mutant strain of Escherichia coli capable of growth on l-1,2-propanediol was isolated previously The mutant is characterized by constitutive production of a propanediol:nicotinamide adenenine dinucleotide (NAD) oxidoreductase which is essential for the new growth property In the present study, it is shown that phage P1 cotransduces the genetic locus conferring this property and the genes for the utilization of l-fucose A further indication of a relationship between these two growth properties is provided by the observation that wild-type E coli excretes propanediol during fermentation of l-fucose Under these conditions, a propanediol dehydrogenase (lactaldehyde reductase) is induced This enzyme migrates on diethylaminoethyl-cellulose with the propanediol dehydrogenase produced constitutively by the mutant strain A key event in the establishment of the ability to grow on propanediol is evidently a shift in the expression and function of propanediol dehydrogenase; an enzyme catalyzing formation of a reduced fermentation product anaerobically in wild-type cells functions aerobically to oxidize this same product in the mutant l-Lactaldehyde, which is thus derived from propanediol, is converted to l-lactate by another dehydrogenase (l-lactaldehyde:NAD oxidoreductase) which is constitutively produced by both wild-type and mutant cells The normal function of this enzyme is not yet established l-Lactate is converted to pyruvate by an inducible NAD-independent l-lactate dehydrogenase Thus, the carbons of propanediol are brought into the central metabolic network of the cell
TL;DR: The results agree with predictions based on the idea that mutations in the structural gene for the enzyme are responsible for the drug-resistant character of these variants.
TL;DR: It is inferred that DCCD restores the capacity of mutant vesicles to establish an electrical potential across the membrane which, in turn, may be the immediate driving force for active transport and other work functions.
TL;DR: It is suggested that in infections defective in late gene expression and consequently in the maturation of replicated DNA, the increased P32 production is caused by the large expansion of the DNA pool.
TL;DR: Preliminary data show similar differences in clonal sensitivity following exposures to DBE, and possibly differences in mutation rates between the two clones after EMS treatment may be associated with a larger amount of heterochromatin or a greater number of SAT-chromosomes in clone 4430.
Abstract: Summary When genes for flower color and other phenotypic characteristics are present in a Heterozygous condition in Tradescantia plants, they can be used as genetic markers for the study of induced mutation. The procedure used is to expose cuttings containing young flower buds to chemical or physical mutagens. 1 to 3 weeks later the resultant mutant pink or colorless cells can be seen in mature flowers, and after relatively simple scoring procedures somatic mutation rates can be calculated. Dose-response curves for ethyl methanesulfonate (EMS) and 1,2-dibromoethane (DBE) were obtained and compared with existing X-ray dose-response curves. Two clones, 02 and 4430 were exposed to known levels (from 5–250 ppm) of EMS in gaseous form for periods of from 1–19 h. After exposure to X-rays pink mutation rates showed similar sensitivities for both clones but the rate for colorless was much higher for clone 4430 and the slope much steeper. After treatment with EMS both colorless and pink rates were appreciably higher for clone 4430 than for clone 02. Preliminary data show similar differences in clonal sensitivity following exposures to DBE. The large differences in mutation rates between loci and between clones after chemical and physical mutagen treatments are not understood at present. Possibly differences in mutation rates between the two clones after EMS treatment may be associated with a larger amount of heterochromatin or a greater number of SAT-chromosomes in clone 4430. The genetic basis for the phenotypic changes (pink and colorless) is not definitely known but may be associated with chromosome breakage, gene mutation, chromosome non-disjunction, or somatic crossing over.
TL;DR: A derivative of the R factor NR1 (called R12) has been isolated which undergoes an increased number of rounds of replication each division cycle in Proteus mirabilis, Escherichia coli, and Salmonella typhimurium.
Abstract: A derivative of the R factor NR1 (called R12) has been isolated which undergoes an increased number of rounds of replication each division cycle in Proteus mirabilis, Escherichia coli, and Salmonella typhimurium. The alteration resulting in the increased number of copies (round of replication mutation) is associated with the transfer factor component of the R factor. R12 has the same drug resistance pattern as NR1, is the same size as shown by sedimentation in a sucrose gradient and electron microscopy (63 × 106 daltons), and has the same partial denaturation map. The level of the R factor gene product chloramphenicol acetyltransferase has been examined in P. mirabilis and was found to be consistent with gene dosage effects. The plasmid to chromosomal deoxyribonucleic acid ratio of NR1 increases several fold after entry into stationary phase, whereas this ratio for R12 remains approximately constant. Individual copies of R12 are selected at random for replication from a multicopy plasmid pool. A smaller percentage of R12 copies replicate during amino acid starvation than has previously been found for NR1 in similar experiments.