Showing papers on "Mutant published in 1970"
TL;DR: Time-lapse photomicroscopy has been utilized to detect temperature-sensitive yeast mutants that are defective in gene functions needed at specific stages of the cell-division cycle to provide two types of information about a mutant: the time at which the defective gene function is normally performed, and the stage at which cells collect when the function is not performed, defined as the termination point.
Abstract: Time-lapse photomicroscopy has been utilized to detect temperature-sensitive yeast mutants that are defective in gene functions needed at specific stages of the cell-division cycle. This technique provides two types of information about a mutant: the time at which the defective gene function is normally performed, defined as the execution point, and the stage at which cells collect when the function is not performed, defined as the termination point. Mutants carrying lesions in three genes that control the cell-division cycle are described. All three genes, cdc-1, cdc-2, and cdc-3, execute early in the cell cycle at about the time of bud initiation, but differ in their termination points. Cells carrying the cdc-1 mutation terminate at the execution point, most cells ending up with a tiny bud that does not develop further. Cells carrying the cdc-2 mutation terminate at mitosis. Cells carrying the cdc-3 mutation are defective in cell separation but show no definite termination point since other processes of the cell cycle, such as bud initiation and nuclear division, continue despite the block in cell separation.
535 citations
TL;DR: The physiological manifestation of conditional lethal mutations in the genes involved in the formation of the T4 head have been re-examined in this paper, where the minimum number of head genes whose active product is needed to form the various head-related structures has been determined by examining infection by a series of double mutants.
378 citations
TL;DR: Kinetic and genetic evidences are presented to show that, in addition to specific amino acid permeases, Saccharomyces cerevisiae has a general amino acids permease which catalyzes the transport of basic and neutral amino acids, but most probably not that of proline.
Abstract: Kinetic and genetic evidences are presented to show that, in addition to specific amino acid permeases, Saccharomyces cerevisiae has a general amino acid permease which catalyzes the transport of basic and neutral amino acids, but most probably not that of proline. The general amino acid permease appears to be constitutive, and its activity is inhibited when ammonium ions are added to the culture medium. A mutant which has lost the general amino acid permease activity was isolated. Its mutation, named gap (general amino acid permease), is not allelic to the aap (amino acid permease) mutation of Surdin et al., which has a quite different phenotype and cannot be considered as having selectively lost the general amino acid permease activity.
335 citations
TL;DR: Seven mutants of E. coli with temperature-sensitive synthesis of DNA have been isolated and it has not yet proved possible to map accurately the mutants showing substantial residual synthesis, and the possibility that these mutations are in a different gene has not been excluded.
Abstract: Seven mutants of E. coli with temperature-sensitive synthesis of DNA have been isolated. Synthesis of RNA, protein and DNA precursors does not appear to be directly affected. The mutants can be divided into at least two groups on the basis of their pattern of DNA synthesis, their ability to support phage growth at 41° and their genetic mapping. Mutants of the first group are heterogeneous in their pattern of DNA synthesis at 40°. Some mutants cease DNA synthesis abruptly upon transfer to 40° and any residual DNA synthesis is barely detectable. In others there is substantial residual synthesis at 40°. All these Group 1 mutants are alike, however, in that they support the growth of phage T4 but not Lambda at 41°. Two mutants with barely detectable residual DNA synthesis carry DNA mutations which have been mapped by P1 transduction and show about 72% linkage to the malB locus. It has not yet proved possible to map accurately the mutants showing substantial residual synthesis, and the possibility that these mutations are in a different gene(s) has not been excluded. A single mutant has been placed in a second group. Like some Group 1 mutants it synthesizes substantial amounts of DNA at 40° before synthesis stops. However, unlike them it supports the growth of T4 and Lambda at 41°. The DNA mutation maps near the leu locus. Certain properties of this mutant are consistent with the idea that initiation of DNA synthesis is temperature-sensitive in this strain.
303 citations
TL;DR: Mutants of five different genes on the X-chromosome of Drosophila melanogaster, having various abnormalities in visual function, have been tested and all have been found to be autonomous, indicating that the primary causes of the behavioral deficits in these mutants are within the eye.
Abstract: Given a mutant having abnormal behavior, the anatomical domain responsible for the deficit may be identified by the use of genetic mosaicism. Individuals may be produced in which a portion of the body is mutant male while the rest is normal female. In such sex mosaics, or gynandromorphs, the division line between normal and mutant parts can occur in various orientations. Mutants of five different genes (cistrons) on the X-chromosome of Drosophila melanogaster, having various abnormalities in visual function, have been tested by this method. All of these have been found to be autonomous, i.e., a mutant eye always functions abnormally, regardless of the amount of normal tissue present elsewhere, indicating that the primary causes of the behavioral deficits in these mutants are within the eye.
293 citations
01 Jan 1970
TL;DR: In his early papers on natural selection, Haldane was concerned with both the dynamics and the statics of evolution, and emphasized that, although evolution depends on changes of gene frequency, nevertheless at any one time the population is in approximate equilibrium for most factors.
Abstract: The basic ideas of genetic load and the cost of natural selection are both from J. B. S. Haldane. In his early papers on natural selection (1924–1932), Haldane was concerned with both the dynamics and the statics of evolution. He emphasized that, although evolution depends on changes of gene frequency, nevertheless at any one time the population is in approximate equilibrium for most factors.
284 citations
TL;DR: The characteristics of a temperature conditional mutant of Escherichia coli K12 indicate that at high temperature, it can complete a DNA cycle already started, but not initiate a new one.
246 citations
TL;DR: A method is described for isolating mutants of Saccharomyces cerevisiae which have lost repressibility by exogenous arginine for ornithine transcarbamylase and three complementary classes of mutations were found: argRI, argRII and argRIII which are recessive and define three loci.
Abstract: A method is described for isolating mutants of Saccharomyces cerevisiae which have lost repressibility by exogenous arginine for ornithine transcarbamylase.
Besides permeability mutants, three complementary classes of mutations were found: argRI, argRII and argRIII which are recessive and define three loci. No evidence for a linkage between any of these three loci or with the gene coding for ornithine transcarbamylase has been obtained.
Strains bearing mutations at either of these loci cannot be distinguished on a phenotype basis: after growth on minimal medium, the l-ornithine carbamoyl transferase activity is twice that of the wild type strain; the mutations modify neither the growth rate nor the permeability to arginine.
The mutations might affect the structure of an hetero-polypeptidic aporepressor.
The level of ornithine transcarbamylase in diploids is proportional to the number of argF+ genes in regulated as well as in non-regulated cells.
246 citations
TL;DR: The product of this gene cro prevents expression of immunity and regulates the expression of those genes to the left of the immunity region in bacteriophage λ.
Abstract: A new gene in bacteriophage λ is described. The product of this gene cro prevents expression of immunity and regulates the expression of those genes to the left of the immunity region. cro- mutants have been isolated and characterized.
222 citations
TL;DR: Temperature-sensitive mutants of vesicular stomatitis virus induced by 5-fluorouracil (FU), 5-azacytidine (ACR), and ethyl methane sulfonate (EMS) have been assigned to four complementation groups by a qualitative test.
Abstract: One hundred and seventy-five temperature-sensitive ( ts ) mutants of vesicular stomatitis virus (type Indiana-C) induced by 5-fluorouracil (FU), 5-azacytidine (ACR), and ethyl methane sulfonate (EMS) have been assigned to four complementation groups by a qualitative test. Group I contains 151 mutants; group II, 2 mutants; group III, 1 mutant; and group IV, 15 mutants; 6 are unclassified. FU was much more effective as a mutagen than either ACR or EMS. The proportion of the mutants belonging to groups I and IV, however, was similar in the case of all three mutagens. Fifteen mutants from groups I and IV have been used to obtain quantitative complementation data. Both groups appear to be homogeneous. Complementation yields increase with increasing multiplicity, but the number of particles per cell required to elicit maximal complementation is small. The pattern of genetic recombination parallels that of complementation. No recombination could be detected in crosses within group I (
222 citations
TL;DR: Mutants of Diplococcus pneumoniae that lacked the two major deoxyribonucleases of the cell were obtained, indicating that a particular cellular component that is susceptible to loss by mutation, such as an enzyme, is responsible for low integration efficiency.
Abstract: Mutants of Diplococcus pneumoniae that lacked the two major deoxyribonucleases of the cell—one an endonuclease, the other an exonuclease preferentially active on native deoxyribonucleic acid (DNA)—were obtained. The development of a method for detecting mutant colonies, based on the binding of methyl green to DNA, facilitated isolation of the mutants. Neither enzyme was essential for growth of the cells, for repair of ultraviolet damage, or for any phase of DNA-mediated transformation. Residual deoxyribonuclease activity in the double mutant corresponded to an exonuclease, approximately one-fifth as active as the major exonuclease, that attacked native and denatured DNA equally well. This activity appeared to be associated with the DNA-polymerase enzyme. A mutant that apparently lacked a cell wall lytic enzyme was also fully transformable. A mutant strain that was four times more sensitive to ultraviolet light than the wild type also transformed normally. Recipient cells of this strain were deficient in the repair of ultraviolet-irradiated transforming DNA. Mutants were found which, unlike the wild type, integrated donor markers only with high efficiency, thereby indicating that a particular cellular component that is susceptible to loss by mutation, such as an enzyme, is responsible for low integration efficiency. Images
TL;DR: Fifty temperature-sensitive mutants defective in DNA synthesis at high temperature have been identified among 655 temperature- sensitive mutants isolated at random from a mutagenised population of B. subtilis, suggesting that at least 14 genes are involved in B.subilis DNA replication.
Abstract: Fifty temperature-sensitive mutants defective in DNA synthesis at high temperature have been identified among 655 temperature-sensitive mutants isolated at random from a mutagenised population of B. subtilis. They are distributed in a non-random fashion in 9 genetic linkage groups, located in different regions of the B. subtilis genome. It is suggested that at least 14 genes are involved in B. subtilis DNA replication.
TL;DR: Three types of mutants were selected in yeast and the mechanisms of their resistance were investigated, finding one is dominant and weakly resistant to 5- fluorouracil, 5-fluorocytosine, and 5- Fluorouridine, and two are recessive and unable to catalyze one of the steps involved in uracil transformation into uridine 5'-monophosphate.
Abstract: Mutants resistant to 5-fluorouracil, 5-fluorocytosine, and 5-fluorouridine were selected in yeast, and the mechanisms of their resistance were investigated. The investigated mutations map in seven different loci. (i) A mutation at the locus FUI 1 gives specifically resistance to 5-fluorouridine. (ii) Two loci are involved in a specific 5-fluorocytosine resistance: a mutation at locus FCY 1 produces a loss of cytosine deaminase activity; a mutation at locus FCY 2 results in the loss of the activity of a cytosine-specific permease. (iii) A mutation at the locus FUR 4 gives a simultaneous resistance to 5-fluorouracil and to 5-fluorouridine by loss in the activity of the uracil-specific permease. (iv) We found three types of mutants in the locus FUR 1. One is dominant and weakly resistant to 5-fluorouracil, 5-fluorocytosine, and 5-fluorouridine. The two others are recessive and are unable to catalyze one of the steps involved in uracil transformation into uridine 5′-monophosphate; this block-age explains their strong resistance to 5-fluorouracil and 5-fluorocytosine. Of these two mutants, one is resistant to 5-fluorouridine and the other is not. (v) Mutations at locus FUR 2 give resistance to 5-fluorouracil, 5-fluorocytosine, and 5-fluorouridine. These mutations are dominant and lead to a loss in the feedback regulation of the aspartic transcarbamylase activity by uridine triphosphate. (vi) The mutants FUR 3 are resistant to 5-fluorocytosine and 5-fluorouridine. They are dominant and physiologically related to the mutants of the locus FUR 1 but their mechanism of resistance is not understood.
TL;DR: A line of polyoma-transformed mouse cells has been isolated which is fully susceptible to lytic infection by polyoma virus and these mutants appear to be blocked at some intracellular step which is required both for the completion of virus development in mouse cells and for transformation in rat or hamster cells.
Abstract: A line of polyoma-transformed mouse cells has been isolated which is fully susceptible to lytic infection by polyoma virus. This line has been used to select virus mutants which have lost most or all of their ability to grow in the untransformed parental line while retaining the ability to grow in the transformed derivative. These virus mutants are also defective in their ability to transform cells of rat or hamster origin. Since the DNA extracted from the mutants has the same host range as the whole virus, the mutants appear to be blocked at some intracellular step which is required both for the completion of virus development in mouse cells and for transformation in rat or hamster cells.
TL;DR: Temperature-sensitive changes of membrane proteins in a previously described temperature-sensitive DNA synthesis mutant were further examined and indicated that X and Y do not have a precursor-product relation, as suggested by the kinetic studies.
TL;DR: All of the temperature-sensitive mutants of Escherichia coli Kl2 carry mutations in the hsm gene, and it is argued that an hsm-directed polypeptide is required for restriction in addition topolypeptides directed by hssK and hsr.
TL;DR: Two mutants with temperature-sensitive suppressor activity specify tRNA's with single base substitutions, giving mispaired bases in the amino acid acceptor arm, including those specifying mutant t RNA's with A · C pairs in helical regions.
TL;DR: Nonsense fragments produced by amber and ochre mutants of the z gene of E. coli are rapidly degraded during exponential growth, while wild type β-galactosidase is stable in the same conditions.
Abstract: Nonsense fragments produced by amber and ochre mutants of the z gene of E. coli are rapidly degraded during exponential growth. Wild type β-galactosidase is stable in the same conditions.
TL;DR: It is concluded that the his-p1 mutant is histidine-permease-less, and that the activity of the histidine permeases are regulated by specific feedback inhibition.
Abstract: Although a large fraction of the histidine accumulated from the medium remains free and intact in Saccharomyces cerevisiae, it is not exchangeable with external histidine. Hence, the steady state concentration level of histidine is not determined by a balance between rates of inflow and outflow.
Preloading the cells with histidine results in a rapid inhibition of histidine uptake, whereas preloading with other amino acids has no effect on histidine uptake.
The inhibition by internal histidine affects the activity, and not the synthesis, of two specific histidine permeases. The histidine permease with high affinity for histidine is much more sensitive to this inhibition than the second histidine permease.
A mutant (his-p1) specifically affected in histidine uptake was isolated.
Criteria for demonstrating that a mutation or a feedback control directly affect an uptake system are discussed.
It is concluded that the his-p1 mutant is histidine-permease-less, and that the activity of the histidine permeases are regulated by specific feedback inhibition.
TL;DR: Using REP− strains derived by transduction, it is obtained no evidence that three rep mutations confer recombination deficiency, although they do do appear to confer a slight increase in UV sensitivity.
TL;DR: A selection technique is used to isolate a new class of lysis-defective mutants of phage T4, the T4 amber t mutants, and it is proposed that the t gene product may be involved in degradation of the host cytoplasmic membrane.
TL;DR: Mutants of Escherichia coli K-12 that grow more slowly in media containing low concentrations of K have been isolated and are therefore referred to as K-dependent, and the abbreviation kdp is proposed for this class of mutant.
Abstract: Mutants of Escherichia coli K-12 that grow more slowly in media containing low concentrations of K have been isolated. All independent mutants of this type which have been studied carry a mutation in a small region of the bacterial chromosome between the supE and gal loci. The growth rate of the mutants is the same as that of the parental strains in medium containing more than 1 mm K, but is only 50% that of the parent when the K concentration is reduced to 0.1 mm. The mutants do not appear to have a primary alteration in K transport, and are therefore referred to as K-dependent. The abbreviation kdp is proposed for this class of mutant.
TL;DR: Functional complementation experiments with λ deletions indicate that xis is located on the λ genome between the int gene and the general recombination gene exo, which probably affects a previously unidentified λ gene, which is designated xis.
TL;DR: “Functional” mutants of phage SP50 are described whose growth, in contrast to wild type SP50, is restricted on B. subtilis strain 168 because of a linear dependence between the number of infected centers and DNA concentration.
Abstract: Summary“Functional” mutants of phage SP50 are described whose growth, in contrast to wild type SP50, is restricted on B. subtilis strain 168. On the basis of complementation tests and genetic crosses, these mutations could be grouped into three genes. Three types of mutants of strain 168, which permitted the growth of any one of the three classes of phage mutants were isolated.In transfection of 168 with SP50 wild type DNA the number of infective centers varies with the third to fourth power of the DNA concentration. Infection of competent 168 cells with an intact functional-mutant phage concomitant with transfection with wild type DNA greatly enhances the specific activity of such DNA and leads to a linear dependence between the number of infected centers and DNA concentration.
TL;DR: It is concluded that recombination is essential to growth because the linear infecting DNA must be circularized by recombination, and circularization is topologically essential to successful replication of the phage genome.
TL;DR: The finding and characterization of the mutants described show that the complete absence of 5-methyluracil and tRNA and 1-methylguanine in rRNA is not lethal, and suggests that different enzymes are responsible for the formation of5-methylURacil in r RNA and t RNA respectively.
TL;DR: An Escherichia coli mutant, extracts of which show no DNA polymerase activity, can excise pyrimidine dimers induced by ultraviolet irradiation, which increases the radiation sensitivity of this strain.
Abstract: An Escherichia coli mutant, extracts of which show no DNA polymerase activity, can excise pyrimidine dimers induced by ultraviolet irradiation The increased radiation sensitivity of this strain is related to the extensive degradation of irradiated DNA
TL;DR: The data suggest that induction of viral multiplication involves the asynchronous occurrence of a unique event, after which DNA synthesis can continue even under non-permissive conditions.
TL;DR: Mutant strains from Salmonella typhimurium and Escherichia coli deficient in either Enzyme I or the phosphate carrier protein of a bacterial phosphotransferase system behaved identically in terms of their growth properties on some carbohydrates, but differed on others.
TL;DR: The results suggest that during growth of Pseudomonas AM1 on C(1) compounds, serine is converted into 3-ph phosphoglycerate by a non-phosphorylated pathway, whereas during growth on succinate, phosphoglycersate is conversion into serine by a phosphorylated pathways.
Abstract: 1. The following enzymes of the phosphorylated pathway of serine biosynthesis have been found in methanol- and succinate-grown Pseudomonas AM1: phosphoglycerate dehydrogenase, phosphoserine-α-oxoglutarate aminotransferase and phosphoserine phosphohydrolase. Their specific activities were similar in the organism grown on either substrate. 2. A procedure for preparation of auxotrophic mutants of Pseudomonas AM1 is described involving N-methyl-N′-nitro-N-nitrosoguanidine as mutagen and a penicillin enrichment step. 3. A mutant, M-15A, has been isolated that is unable to grow on methanol and that lacks phenazine methosulphate-linked methanol dehydrogenase. The mutant is able to grow on methylamine, showing that the amine is not oxidized by way of methanol. 4. Loss of methanol dehydrogenase activity in mutant M-15A led to loss of phenazine methosulphate-linked formaldehyde dehydrogenase activity showing that the same enzyme is probably responsible for both activities. 5. A mutant, 20B-L, has been isolated that cannot grow on any C1 compound tested but can grow on succinate. 6. Mutant 20B-L lacks hydroxypyruvate reductase, and revertants that regained the ability to grow on methanol, methylamine and formate contained hydroxypyruvate reductase activity at specific activities similar to that of the wild-type organism. This shows that hydroxypyruvate reductase is necessary for growth on methanol, methylamine and formate but not for growth on succinate. 7. The results suggest that during growth of Pseudomonas AM1 on C1 compounds, serine is converted into 3-phosphoglycerate by a non-phosphorylated pathway, whereas during growth on succinate, phosphoglycerate is converted into serine by a phosphorylated pathway.