Showing papers on "Mutant published in 1975"
TL;DR: It is suggested that the transformation process may require two distinct events, each related to A gene expression, which depended both on the nature of the A mutation in a given cell species and on the species of the cell transformed by a given mutant.
Abstract: In productive infection by simian virus 40, the A gene is known to regulate the initiation of viral DNA replication and to control the synthesis of late viral RNA. The function of the A gene in transforming infection was investigated by the infection of a variety of cell species with six independently isolated temperature-sensitive mutants belonging to the A complementation group. The A mutants failed to initiate the stable transformation of cells during continuous infection at the restrictive temperature. After the establishment of transformation at the permissive temperature and a subsequent shift to the restrictive temperature to block the A function, however, two distinct virus-cell interactions were identified. In one case, the increased colony-forming capacity of transformed cells remained stable after the temperature shift. In the other case, the temperature shift decreased the capacity of transformed cells to form colonies to the level of untransformed control cells. The outcome of the virus-cell interaction depended both on the nature of the A mutation in a given cell species and on the species of the cell transformed by a given mutant. These findings suggest that the transformation process may require two distinct events, each related to A gene expression.
403 citations
TL;DR: Thirty-five temperature-sensitive mutants of Aspergillus nidulans which are defective in nuclear division, septation or distribution of nuclei along the mycelium have been isolated, and most have been subjected to complementation analysis and mapped to chromosome.
Abstract: Forty-five temperature-sensitive mutants of Aspergillus nidulans which are defective in nuclear division, septation or distribution of nuclei along the mycelium have been isolated, and most have been subjected to complementation analysis and mapped to chromosome. Thirty-five of the mutants were unable to complete nuclear division at the restrictive temperature. Twenty-six of these mutants exhibited a co-ordinate drop in both spindle and chromosome mitotic indices at 42 °C, indicating that they fail to enter mitosis. These mutants have been assigned to the gene symbol nim. Nine mutants exhibited a co-ordinate rise in spindle and chromosome mitotic indices at 42 °C, indicating that they are arrested in mitosis. These mutants were assigned the gene symbol bim. Five mutants failed to form septa and were given the gene symbol sep; and five mutants had an abnormal nuclear distribution and were given the gene symbol nud. All of the mutations were recessive. Most of the mutants were in different complementation groups. Mutants in the same complementation groups were phenotypically similar, but phenotypically similar mutants were not necessarily or usually in the same complementation group. There was no evidence for genetic clustering of phenotypically similar mutants. The mutants were located on all eight chromosomes.
305 citations
TL;DR: The purpose of the experiments described was to identify X chromosome genes functioning mainly or exclusively during oogenesis, leading to an estimation of a total of about 150 X-linked genes involved in female fertility.
Abstract: The purpose of the experiments described was to identify X chromosome genes functioning mainly or exclusively during oogenesis. Two mutagenesis experiments were carried out with ethyl methane sulfonate. Following treatment inducing 60% lethals, 9% of the treated X chromosomes carried a female sterility mutation which did not otherwise seriously affect viability. Among--95 isolated mutants, 19 were heat-sensitive and 5 cold-sensitive. The mutants have been classified as follows: I (16 mutants; 12 complementation groups): the females laid few or no eggs; the defect concerned either ovulation or oogenesis. II (37 mutants; 18 complementation groups): the female laid morphologically abnormal eggs, often with increased membrane permeability. III A (13 mutants; at least 8 complementation groups): the homozygous females were sterile if mated to mutant males; their progeny (homo- and hemizygous) died at a late embryonic stage (11 mutants), at the larval stage (1 mutant) or at the pupal stage (1 mutant). However fertility was partly restored by breeding to wild-type males as shown by survival of some heterozygous descendants. III B (29 mutants; 22 complementation groups): the fertility of the females was not restored by breeding to a wild-type male. Most of the eggs of 13 of the mutants died at a late stage of embryogenesis. The eggs of the others ceased development earlier or, perhaps, remained unfertilized. The distribution of the number of mutants per complementation group led to an estimation of a total of about 150 X-linked genes involved in female fertility. The females of three mutants, heat-sensitive and totally sterile at 29 degrees, produced at a lower temperature descendants morphologically abnormal or deprived of germ cells. Three other mutants not described in detail showed a reduction in female fertility with many descendants lacking germ cells. A desirable mutant which was not recovered was one with normal fertile females producing descendants which, regardless of their genotype, bore specific morphological abnormalities. The value of the mutants isolated for analysis of the complex processes leading to egg formation and initiation of development is discussed.
298 citations
TL;DR: Transformants isolated after infection of rat embryo cells at 33 C with either wild-type simian virus 40 or with the temperature-sensitive gene A mutants, tsA7 and tsA28 suggest that an active A function is required for the maintenance of transformation in these cells.
Abstract: Transformants have been isolated after infection of rat embryo cells at 33 C with either wild-type simian virus 40 or with the temperature-sensitive gene A mutants, tsA7 and tsA28. Examination of properties usually associated with transformation such as growth in 1% serum, growth rate, saturation density, and morphology show that these properties are temperature dependent in the tsA transformants characterized, but are not temperature dependent in the wild-type transformants that have been examined. In the most thoroughly characterized tsA transformants the expression of T antigen also appears to be temperature dependent. These data suggest that an active A function is required for the maintenance of transformation in these cells. In the lytic cycle, the A function is involved in the initiation of DNA synthesis. Thus transformation by simian virus 40 may be the direct consequence of the introduction of the simian virus 40 replicon and the presence of its DNA initiator function, which causes the cell to express a transformed phenotype.
267 citations
TL;DR: Mutants of Saccharomyces cereviaiae showing defects in cytochrome oxidase, coenzyme QH2-cytochrome c reductase, and rutamycin-sensitive ATPase are described and are established to be nuclear.
243 citations
TL;DR: The relationship between photoexcitation of the visual pigment and the production of quantum bumps is investigated using a mutant of Drosophila melanogaster—a third chromosome recessive mutant described by Cosens and Manning7, in which the electroretinogram decays to baseline during a strong, prolonged stimulus.
Abstract: RANDOMLY occurring, discrete voltage fluctuations (quantum bumps) have been recorded in photoreceptors of several arthropods1–4 It is thought that these bumps sum to produce the receptor potential5,6 We have investigated the relationship between photoexcitation of the visual pigment and the production of quantum bumps using a mutant of Drosophila melanogaster—a third chromosome recessive mutant described by Cosens and Manning7, in which the electroretinogram decays to baseline during a strong, prolonged stimulus We will call this mutant the transient receptor potential mutant (trp)
238 citations
TL;DR: Techniques are described for the use of various yeast strains to detect the induction of (1)Mitotic crossing-over, (2) mitotic gene conversion, (3) forward mutation and (4) reverse mutation.
Abstract: Techniques are described for the use of various yeast strains to detect the induction of (1) mitotic crossing-over, (2) mitotic gene conversion, (3) forward mutation and (4) reverse mutation. The technique for the detection of mitotic crossing over is based on a diploid that carries two different alleles of the gene locus ade2. These alleles differ in their extent of colony pigmentation engendered on low-adenine media, and they complement each other to the effect that the diploid is white. Mitotic crossing over results in the formation of twin-sectored colonies with a red and a pink sector. The technique for the detection of mitotic gene conversion is based on the use of a heteroallelic diploid carrying two non-complementing alleles that cause a nutritional requirement. Mitotic gene conversion leads to the restoration of intact and dominant wild-type alleles that alleviate the nutritional requirement so that convertant cells can be selected on a minimal medium. The forward mutation technique is based on the use of a haploid strain with a defect in the ade2-gene locus which causes the formation of red colonies. Induction of forward mutation in a number of other loci prevents the accumulation of this red pigment so that induction of mutation can be detected by the formation of pink and white colonies. The reverse mutation technique is based on the restoration or compensation of a mutational defect causing a growth requirement. Mutants can be selected for a minimal medium.
230 citations
TL;DR: Results are taken to indicate that the H5 ts125 mutant codes for a DNA binding protein that is thermolabile for continued binding to single-stranded DNA.
Abstract: Infection of African green monkey kidney cells with type 5 adenovirus leads to the synthesis of two infected, cell-specific proteins with approximate molecular weights of 72,000 and 48,000, that bind specifically to single-stranded but not double-stranded DNA. The production of these two proteins was studied after infection with two DNA-negative adenovirus mutants belonging to different complementation groups (H5 ts36 and H5 ts 125). Both DNA binding proteins were detected in cells infected with either mutant at the permissive temperature (32 C) AND ALSO IN H5 ts36-infected cells at the nonpermissive temperature (39.5 C). In H5 ts125-infected cells at 39.5 C, however, less than 5% of the normal wild-type level of these DNA binding proteins was detectable. When H5 ts125-infected cells were labeled with radioactive leucine at 32 C and subsequently shifted to 39.5 C in the presence of unlabeled leucine (chase), the level of DNA binding proteins found in these infected cells was markedly reduced compared to cultures not shifted to 39.5 C. These data suggest that the DNA binding proteins themselves were temperature sensitive. This conclusion was confirmed by experiments in which the DNA binding proteins were eluted from DNA cellulose with buffers of increasing temperatures (thermal elution). The H5 ts 125 proteins were shown to elute at lower temperatures than either wild-type or H5 ts36 proteins. These results are taken to indicate that the H5 ts125 mutant codes for a DNA binding protein that is thermolabile for continued binding to single-stranded DNA.
228 citations
TL;DR: Investigation of the timing, kinetics, and extent of cell death revealed that losses in cell viability in the range of 2-4 log orders could be prevented by the addition of inositol to the medium or by disruption of protein synthesis with cycloheximide.
Abstract: Fifty-two inositol-requiring mutants of Saccharomyces cerevisiae were isolated following mutagenesis with ethyl methanesulfonate. Complementation and tetrad analysis revealed ten major complementation classes, representing ten independently segregating loci (designated ino1 through ino10) which recombined freely with their respective centromeres. Members of any given complementation class segregated as alleles of a single locus. Thirteen complementation subclasses were identified among thirty-six mutants which behaved as alleles of the ino1 locus. The complementation map for these mutants was circular. - Dramatic cell viability losses indicative of unbalanced growth were observed in liquid cultures of representative mutants under conditions of inositol starvation. Investigation of the timing, kinetics, and extent of cell death revealed that losses in cell viability in the range of 2-4 log orders could be prevented by the addition of inositol to the medium or by disruption of protein synthesis with cycloheximide. Mutants defective in nine of the ten loci identified in this study displayed these unusual characteristics. The results suggest an important physiological role for inositol that may be related to its cellular localization and function in membrane phospholipids. The possibility is discussed that inositol deficiency initiates the process of unbalanced growth leading to cell death through the loss of normal assembly, function, or integrity of biomembranes. - Part of this work has been reported in preliminary form (CULBERTSON and HENRY 1974).
228 citations
TL;DR: Genetic analysis showed that two genes control synthesis of the glucose repressible enzyme ADHII, one gene the constitutive ADHI and a fourth nuclear gene the mitochondrial ADH showed any linkage.
Abstract: On the basis of allyalcohol resistance, Saccharomyces cerevisiae mutanta were isolated that were deficient in alcohol dehydrogenase (ADH). The mutants were divided into three classes by their different ADH isozyme pattern obtained after starch-gel electrophoresis: adc mutants that did not produce the constitutive ADH, adr mutants from which the glucose repressible enzyme (ADHII) was absent, and adm mutants deficient in ADH activity associated with the mitochondria. Genetic analysis showed that two genes control synthesis of the glucose repressible enzyme ADHII, one gene the constitutive ADHI and a fourth nuclear gene the mitochondrial ADH. None of these four genes showed any linkage. The various mutant types did not show drastic effects on yeast growth on media containing glucose or ethanol as sole carbon sources.
223 citations
TL;DR: It is shown that genetic reversion of missense mutants can be of value in producing new temperature-sensitive and cold-sensitive mutations affecting related functions and it is suggested that the approach can be extended to organisms with large genomes.
Abstract: An analysis of revertants of missense mutants in phage P22 has shown: (i) New temperature-sensitive (TS) and cold-sensitive (CS) phenotypes are often acquired concomitant with reversion. (ii) In many cases, these new phenotypes are due to second-site mutations (suppressors) that correct the original defect. (iii) Sometimes the suppressor mutation is not in the same gene as the original mutation. (iv) Extragenic suppressors are almost always in genes whose products are known to interact physically with the original gene products. (v) The suppressor mutations typically retain their TS or CS phenotypes when crossed into wild-type genetic backgrounds. (vi) Some TS and CS mutants derived by reversion can themselves be reverted to produce additional mutations. We have shown that genetic reversion of missense mutants can be of value in producing new temperature-sensitive and cold-sensitive mutations affecting related functions. We suggest that our approach can be extended to organisms with large genomes.
TL;DR: Sedimentation profiles suggest that the rad 52 mutant lacks a repair system for X-ray induced damage and are consistence with the proposal that an unrepaired chromosome break leads to reproductive cell death.
Abstract: Sedimentation profiles for chromosomal DNA from unirradiated and X-irradiated yeast cells of wild type and rad 52 strains are presented. These profiles indicate that, whereas wild type strains rejoin DNA double-strand breaks, rad 52 strains apparently do not. These data suggest that the rad 52 mutant lacks a repair system for X-ray induced damage and are consistent with the proposal that an unrepaired chromosome break leads to reproductive cell death.
TL;DR: It is concluded that in rep mutants the speed of replication fork movement is only 50 to 60% of that of wild-type cells.
TL;DR: In the course of searching for T7 mutants that are unable to overcome restriction, it was discovered that mutants defective in gene 2 are able to plate on E. coli C with essentially normal efficiency, and most gene 7 mutants are ableto plate on both C and K strains.
TL;DR: It must be concluded that the protective role of glutathione is only significant when a chemical challenge is present.
TL;DR: Application of the Newcombe respreading experiment demonstrates that the [URES3] mutational event occurs before the selection procedure and is therefore not strictly adaptative, Nevertheless, the nature of the selection medium changes considerably the frequency of the [URE3] mutants recovered.
Abstract: [URE3], a non-mitochondrial non-mendelian mutation which modifies drastically yeast nitrogen metabolism has been genetically studied. Cytoduction experiments show definitely that the inheritance of the determinant is not linked to the nucleus. The maintenance of the [URE3] determinant seems controlled by the product of a conventional nuclear gene (ure2) which is itself involved in nitrogen metabolism. The (ure2) mutation alone gives the same phenotype as [URE3] but it is impossible to obtain a stable recombinant containing simultaneously the (ure2) mutation and the [URE3] determinant. Application of the Newcombe respreading experiment demonstrates that the [URE3] mutational event occurs before the selection procedure and is therefore not strictly adaptative. Nevertheless, the nature of the selection medium changes considerably the frequency of the [URE3] mutants recovered.
TL;DR: It is concluded that the reaction of DCCD with this specific protein leads to inhibition of the ATP energy-transducing reactions.
Abstract: Membranes of Escherichia coli contain an adenosine 59-triphosphate (ATP) energy-transducing system that is inhibited by treatment with dicyclohexylcarbodiimide (DCCD) The carbodiimide-reactive protein component of this system has been identified after treatment with [14C]DCCD This protein has an apparent molecular weight of 9,000 as judged from acrylamide gel electrophoresis in the presence of sodium dodecyl sulfate and is extracted from the membrane with chloroform-methanol (2:1) These properties are similar to the analogous protein previously identified in mitochondria (Cattell et al, 1971) A mutant strain, RF-7, has been isolated which derives energy from oxidative phosphorylation in the presence of 5 mM DCCD The ATP hydrolase activity of the membraned system in the mutant was considerably less sensitive to inhibition by DCCD than that in the wild type The carbodiimide-reactive protein, which was easily labeled by [14C]DCCD in the wild type, was labeled much less rapidly in the carbodiimide-resistant mutant It is thus concluded that the reaction of DCCD with this specific protein leads to inhibition of the ATP energy-transducing reactions The mutation causing carbodiimide resistance in strain RF-7 was mapped It is cotransduced with the uncA gene at a frequency exceeding 90% The mutationally altered protein causing the carbodiimide resistance was not conclusively identified However, reconstitution experiments indicate that the altered protein is not one of the subunits of the soluble ATP hydrolase activity, which can be removed from the membrane by washing with 1 mM tris(hydroxymethyl)aminomethane buffer lacking Mg2+ The carbodiimide-reactive protein remains with the membrane residue after removal of the soluble ATP hydrolase and is thus distinct from these subunits as well Images
TL;DR: The meiotic spore progeny obtained by mating the mutants to a respiratory competent haploid yeast, when scored for growth on glycerol, show a non-Mendelian segregation of the phenotype, indicating the mutations to be cytoplasmically inherited.
TL;DR: Temperature-sensitive mutants of simian virus 40 (SV40), representing each complementation class, have been mapped by marker rescue with Endo R fragments of wild-type SV40-DNA suggesting that B, C, and BC mutations are in one cistron, complementation occurring at the protein level.
TL;DR: The induction of host DNA synthesis is impaired when cultures are infected with mutants of the A group at 42.5 C rather than 40 C, suggesting that the A function may be responsible for host induction.
Abstract: Host DNA synthesis is induced when CV-1 (monkey kidney) cell cultures are infected at 40 C with wild-type virions or with temperature-sensitive Simian virus 40 mutants of the "early" complementation group A. Host DNA synthesis is not induced when cultures are infected with mutants of the late complementation group D. The simplest explanation for these observations, that induction depends not upon the expression of some early gene function but rather on the presence of an active D protein in the infecting virion, has been examined. Indirect experiments suggest that this explanation is not correct. Moreover, the induction of host DNA synthesis is impaired when cultures are infected with mutants of the A group at 42.5 C rather than 40 C, suggesting that the A function may be responsible for host induction. The inability of D virions to induce host DNA synthesis may reflect their inability to "uncoat" at 40C.
TL;DR: Property of a non-Mendelian, cytoplasmic mutant is reported, which can be of practical importance for producing mutant plants of economic value by tissue culture techniques.
Abstract: THE possibility of producing mutant plants of economic value by tissue culture techniques has attracted considerable interest and discussion1–6, and was confirmed by the regeneration of plants from mutant cell lines1. The isolation of cytoplasmic mutants (all of those studied so far have carried Mendelian traits1,2) can be of practical importance; for example, male sterile ones in maize may be used for producing hybrid seeds. We report here, however, properties of a non-Mendelian, cytoplasmic mutant.
TL;DR: For example, the authors showed that mutations affecting an enzyme II-complexmt1 activity of the phosphoenolpyruvate-dependent phosphotransferase system all map in gene mtlA. This gene has previously been shown (Solomon and Lin, 1972) to be part of an operon, mtl, located at 71 min on the E. coli linkage map.
Abstract: Mutants of Escherichia coli K-12 unable to grow on any of the three naturally occurring hexitols D-manitol, D-glucitol, and galactitol and, among these specifically, mutants with altered transport and phosphorylating activity have been isolated. Different isolation procedures have been utilized, including suicide by D-[3H]mannitol, chemotaxis, and resistance to the toxic hexitol analogue 2-deoxy-arabino-hexitol. Mutations thus obtained have been mapped in four distinct operons. (i) Mutations affecting an enzyme II-complexmt1 activity of the phosphoenolpyruvate-dependent phosphotransferase system all map in gene mtlA. This gene has previously been shown (Solomon and Lin, 1972) to be part of an operon, mtl, located at 71 min on the E. coli linkage map containing, in addition to mtlA, the cis-dominant regulatory gene mtlC and mtlD, the structural gene for the enzyme D-mannitol-1-phosphate dehydrogenase. The gene order in this operon, induced by D-mannitol, is mtlC A D. (ii) Mutations in gene gutA affecting a second enzyme II-complexgut of the phosphotransferase system map at 51 min, clustered in operon gutC A D together with the cis-dominant regulatory gene gutC and the structural gene gutD for the enzyme D-glucitol-6-phosphate dehydrogenase. The gut operon, previously called sbl or srl, is induced by D-glucitol. (iii) Mutations affecting the transport and catabolism of galactitol are clustered in a third operon, gatC A D, located at 40.5 min. This operon again contains a cis-dominant regulatory gene, gatC, the structural gene gatD for galactitol-1-phosphate dehydrogenase, and gene gatA coding for a thrid hexitol-specific enzyme II-complexgat. Other genes coding for two additional enzymes involved in galactitol catabolism apparently are not linked to gatC A D. (iv) A fourth class of mutants pleiotropically negative for hexitol growth and transport maps in the pts operon. Triple-negative mutants (mtlA gutA gatA) do not have further transport or phosphorylating activity for any of the three hexitols.
01 Dec 1975-Canadian journal of genetics and cytology. Journal canadien de génétique et de cytologie
TL;DR: A model for colchicine-resistance is proposed which suggests that certain membrane proteins such as the new glycoprotein of CHR cells, are modulators of membrane fluidity (mmf proteins) whose molecular conformation regulates membrane permeability to a variety of compounds and that the CHR mutants are altered in their mmf proteins.
Abstract: Independent colchicine-resistant (CHR) mutants of Chinese hamster ovary cells displaying reduced permeability to colchicine have been isolated. A distinguishing feature of these membrane-altered mutants is their pleiotropic cross-resistance to a variety of unrelated compounds. Genetic characterization of the CHR lines indicate that colchicine resistance and cross-resistance to other drugs are of a dominant nature in somatic cell hybrids. Revertants of CHR have been isolated which display decreased resistance to colchicine and a corresponding decrease in resistance to other drugs. These results strongly suggest that colchicine resistance and the pleiotropic cross-resistance are the result of the same mutation(s). Biochemical studies indicate that although colchicine is transported into our cells by passive diffusion, no major alterations in the membrane lipids could be detected in mutant cells. However, there appears to be an energy-dependent process in these cells which actively maintains a permeability barrier against colchicine and other drugs. The CHR cells might be altered in this process. A new glycoprotein has been identified in mutant cell membranes which is not present in parental cells, and is greatly reduced in revertant cells. A model for colchicine-resistance is proposed which suggests that certain membrane proteins such as the new glycoprotein of CHR cells, are modulators of membrane fluidity (mmf proteins) whose molecular conformation regulates membrane permeability to a variety of compounds and that the CHR mutants are altered in their mmf proteins. The possible importance of the CHR cells as models for investigating aspects of chemotherapy related to drug resistance is discussed.
TL;DR: The results taken together with those of the previous papers show that the overall pathway for the morphogenesis of the T4 baseplate represents the aggregation of six 15 S arm complexes around a central 22 S hub structure.
TL;DR: The results suggest that a somatic mutation leads to a defect of the protein kinase regulatory subunit and that activity of this kinase is required for induction of cell death by cyclic AMP.
Abstract: Dibutyryl cyclic AMP and theophylline kill S491 mouse lymphoma tissue culture cells When cells are grown in soft agar with these drugs, the few clones that survive are resistant to cytolysis The rate of mutation to resistance is 1-3 times 10-7/cell/generation in both diploid and tetraploid cells The incidence of mutants is increased by treatment with a chemical mutagen, ICR 191 The mutation is consistently associated with greatly reduced or absent cytoplasmic cyclic AMP binding protein These results suggest that a somatic mutation leads to a defect of the protein kinase regulatory subunit and that activity of this kinase is required for induction of cell death by cyclic AMP
TL;DR: A selection procedure is described which permits a large number of Saccharomyces cerevisiae mutants to be screened for specific lesions in mitochondrial respiratory enzymes and the adenosine triphosphatase and two cytoplasmic mutants have been found whose primary defect is in cytochrome oxidase.
Abstract: A selection procedure is described which permits a large number of Saccharomyces cerevisiae mutants to be screened for specific lesions in mitochondrial respiratory enzymes and the adenosine triphosphatase. The method has been used to isolate nuclear mutant strains with specific lesions in coenzyme QH2-cytochrome c reductase, cytochrome oxidase, and adenosine triphosphatase. In addition, two cytoplasmic mutants have been found whose primary defect is in cytochrome oxidase, and others have been found that show variable degrees of abnormalities in their mitochondrial translation products.
TL;DR: The results suggest that there are two influenza viral gene functions required for transcription and most likely two additional gene functions needed for RNA replication.
Abstract: Influenza WSN virus temperature-sensitive (ts) mutants were examined for defects in viral complementary RNA (cRNA) synthesis. The synthesis of viral cRNA was determined by hybridizing RNA from infected cells to radiolabeled virion RNA of known specific activity. Mutants in complementation groups I and III synthesized little, or no, cRNA at the nonpermissive temperature (39.5 C). When cells infected by these mutants were incubated for 5 h at the permissive temperature (33 C) and were then shifted to 39.5 C, net synthesis of cRNA ceased. This strongly suggests that mutants in these two complementation groups possess a ts defect in the transciptase complex. Mutants in group II and group V synthesize reduced amounts of cRNA at 39.5 C. In contrast to the group I and group III mutants, cRNA synthesis in cells infected by a group II or a group V mutant continues after a shift-up. This indicated that these mutants do not possess a ts transcriptase complex and that these mutants are most probably defective in some step in the amplification of cRNA synthesis. As will be discussed, the most likely defect in these mutants is in the synthesis of virion-type RNA. These results suggest that there are two influenza viral gene functions required for transcription and most likely two additional gene functions required for RNA replication.
TL;DR: Investigation of various amdR; areA double mutants has led to the conclusion that amdR and areA participate in independent regulatory circuits in the control of acetamide utilization, indicating that areA is involved in derepression of acetamidase upon relief of ammonium repression.
Abstract: Mutants of Apergillus nidulanswith lesions in a gene, areA (formerly called amdT), have been isolated by a variety of different selection methods. The areA mutants show a range of pleiotropic growth responses to a number of compounds as sole nitrogen sources, but are normal in utilization of carbon sources. The levels of two amidase enzymes as well as urease have been investigated in the mutants and have been shown to be affected by this gene. Most of the areA mutants have much lower amidase-specific activities when grown in ammonium-containing medium, compared with mycelium incubated in medium la9king a nitrogen source. Some of the areA. mutants do not show derepression of urease upon relief of ammonium repression. The dominance relationships of areA alleles have been investigated in· heterozygous diploids, and these studies lend support to the proposal that areA codes for a positively acting regulatory product. One of the new areA alleles is partially dominant to areA + and areA102. This may be a result of negative complementation or indicate that areA has an additional negative reiuIatory function. Investigation.of various amdR; areA double mutants has led to the conclusion that amdR and areA participate in independent regulatory circuits in the control of acetamide utilizatiol1. Studies on an amdRc; areA.double mutant indicate that areA is involved in derepression of acetamidase upon relief of ammo.nium repression.
TL;DR: Fifteen temperature-sensitive mutants of herpes simplex virus type 1 were studied with regard to the relationship between their ability to synthesize viral DNA and to induce viral DNA polymerase (DP) activity at permissive and nonpermissive temperatures.
Abstract: Fifteen temperature-sensitive mutants of herpes simplex virus type 1 were studied with regard to the relationship between their ability to synthesize viral DNA and to induce viral DNA polymerase (DP) activity at permissive (34 C) and nonpermissive (39 C) temperatures. At 34 C, all mutants synthesized viral DNA, while at 39 C four mutants demonstrated a DNA+ phenotype, three were DNA+/-, and eight were DNA-. DNA+ mutants induced levels of DP activity similar to thhose of the wild-type virus at both temperatures, and DNA+/- mutants induced reduced levels of DP activity at 39 C but not at 34 C. Among the DNA- mutants three were DP+, two were DP+/-, and three showed reduced DP activity at 34 C with no DP activity at 39 C. DNA-, DP- mutants induced the synthesis of a temperature-sensitive DP as determined by in vivo studies.
TL;DR: The development of a system for the detection of somatic cell mutation to hypoxanthine-guanine-phosphoribosyl-transferase (HGPRT) and the selection of mutant cells was not influenced by the concentration of the selective agent 6-thioguanine, and the optimal expression time for TGr-resistant mutants in L5178Y cells was 6 to 7 days.
Abstract: The development of a system for the detection of somatic cell mutation to hypoxanthine-guanine-phosphoribosyl-transferase (HGPRT) (EC 2.4.2.8) deficiency in L5178Y mouse lymphoma cells is described. The selection of mutant cells was not influenced by the concentration of the selective agent 6-thioguanine (6-TG). In addition, all the mutants selected, spontaneous as well as induced ones, showed a complete loss of HGPRT activity. In reconstruction experiments, in which mutant cells were mixed with wild-type cells, the recovery of mutant cells was only markedly influenced when wild-type cells were seeded in a cell density ten times higher than the one, 5·10 4 cells/ml, used in subsequent induction experiments. X-irradiation and treatment with ethyl methanesulfonate (EMS) increased the mutation rate above the spontaneous background. A clear-cut dose-dependent mutagenic effect after exposure to X-rays was measured. The rate of induced mutations at the HGPRT locus in lymphoma cells was 1–3·10 −7 per R, as determined after exposures of 200, 300, 400, 500 and 600 R. The time the cells needed to express their mutations was much longer than 48 h. Further study of this phenomenon showed that the optimal expression time for TG r - resistant mutants in L5178Y cells was 6 to 7 days. No indication for a dose-dependent effect on the optimal expression of the mutants was found.