Effects Of Gene Mutations Research Articles

Effect of Mutations in Genes Affecting Homologous Recombination on Restriction Enzyme-Mediated and Illegitimate Recombination in Saccharomyces cerevisiae

Restriction enzyme-mediated events (REM events; integration of transforming DNA catalyzed by in vivo action of a restriction enzyme) and illegitimate recombination events (IR events; integration of transforming DNA that shares no homology with the host genomic sequences) have been previously characterized in Saccharomyces cerevisiae. This study determines the effect of mutations in genes that are involved in homologous recombination and/or in the repair of double-stranded DNA breaks on these recombination events. Surprisingly, REM events are completely independent of the double-strand-break repair functions encoded by the RAD51, RAD52, and RAD57 genes but require the RAD50 gene product. IR events are under different genetic control than homologous integration events. In the rad50 mutant, homologous integration occurred at wild-type frequency, whereas the frequency of IR events was 20- to 100-fold reduced. Conversely, the rad52 mutant was grossly deficient in homologous integration (at least 1,000-fold reduced) but showed only a 2- to 8-fold reduction in IR frequency.

Effect of mutations in genes affecting homologous recombination on restriction enzyme-mediated and illegitimate recombination in Saccharomyces cerevisiae.

Restriction enzyme-mediated events (REM events; integration of transforming DNA catalyzed by in vivo action of a restriction enzyme) and illegitimate recombination events (IR events; integration of transforming DNA that shares no homology with the host genomic sequences) have been previously characterized in Saccharomyces cerevisiae. This study determines the effect of mutations in genes that are involved in homologous recombination and/or in the repair of double-stranded DNA breaks on these recombination events. Surprisingly, REM events are completely independent of the double-strand-break repair functions encoded by the RAD51, RAD52, and RAD57 genes but require the RAD50 gene product. IR events are under different genetic control than homologous integration events. In the rad50 mutant, homologous integration occurred at wild-type frequency, whereas the frequency of IR events was 20- to 100-fold reduced. Conversely, the rad52 mutant was grossly deficient in homologous integration (at least 1,000-fold reduced) but showed only a 2- to 8-fold reduction in IR frequency.

Effect of mutations in genes affecting homologous recombination on restriction enzyme-mediated and illegitimate recombination in Saccharomyces cerevisiae.

Effect of mutations in genes affecting homologous recombination on restriction enzyme-mediated and illegitimate recombination in Saccharomyces cerevisiae.

Session 9: Expression and Tissue-Specific Consequences of Gene Mutations of Extracellular Matrix Genes

Session 9: Expression and Tissue-Specific Consequences of Gene Mutations of Extracellular Matrix Genes

Effects of gene mutations in lipoprotein and hepatic lipases as interpreted by a molecular model of the pancreatic triglyceride lipase.

A molecular model of human pancreatic lipase (Winkler, F. K., D'Arcy, A., and Hunziker, W. (1990) Nature 343, 771-774) is used to explain the possible structural effects of the amino acid mutations identified to date in the human lipoprotein and hepatic lipase genes. A sequence homology profile was used to evaluate the alignment of the amino acid sequences of all three lipolytic enzymes (Kirchgessner, T. G., Chuat, J.-C., Heinzmann, C., Etienne, J., Guilhot, S., Svenson, K., Ameis, D., Pilon, C., D'Auriol, L., Andalibi, A., Schotz, M. C., Galibert, F., and Lusis, A. J. (1989) Proc. Natl. Acad. Sci. U. S. A. 86, 9647-9651) with respect to the secondary structure elements identified in the pancreatic lipase. As expected, maximum homology is observed in internal regions namely the hydrophobic strands of the central beta-pleated sheet. This observation strongly supports the hypothesis that all three molecules exhibit a very similar three-dimensional structure, particularly in the N-terminal catalytic domain. There is considerable variation in some of the surface loops connecting the individual strands, whereas others are conserved. It is hypothesized that the most conserved loops located around the active site are responsible for the catalytic function (similar for all three enzymes), whereas those that markedly differ are involved in the regulation at the molecular level, namely the binding of colipase (pancreatic enzyme) and apolipoprotein CII (lipoprotein lipase). The currently available library of hepatic and lipoprotein gene mutations seems to indicate that the majority of mutants disrupt the folding of the polypeptide chain, rather than affect specific constellations in and around the catalytic site or regulatory loops.

Induction of the SOS response by hydrogen peroxide in various Escherichia coli mutants with altered protection against oxidative DNA damage

The induction of the SOS response by H2O2 was measured in Escherichia coli by means of a sfiA::lacZ operon fusion. The effects of mutations in genes involved in DNA repair or DNA metabolism on the SOS response were investigated. We found that in an uvrA mutant, H2O2 induced the SOS response at lower concentrations than in the uvr+ parent strain, indicating that some lesions induced by H2O2 may be repaired by the uvrABC-dependent excision repair system. A nth mutation, yielding deficiency in thymine glycol DNA glycosylase, had no detectable effect on SOS induction, indicating that thymine glycol, a DNA lesion expected to be induced by H2O2, does not participate detectably in the induction of the SOS response by this chemical under our conditions. H2O2 still induced the SOS response in a dnaC(Ts) uvrA double mutant under conditions in which no DNA replication proceeds, suggesting that this chemical induces DNA strand breaks. Induction of the SOS response by H2O2 was also assayed in various mutants affected in genes suspected to be important for protection against oxidative stress. Mutations in the catalase genes, katE and katG, had only minor effects. However, in an oxyR deletion mutant, in which the adaptative response to H2O2 does not occur, SOS induction occurred at much lower H2O2 concentrations than in the oxyR+ parent strain. These results indicate that some enzymes regulated by the oxyR gene are, under our conditions, more important than catalase for protection against the H2O2-induced DNA damages which trigger the SOS response.

The genetic dependence of recombination in recD mutants of Escherichia coli.

RecBCD enzyme has multiple activities including helicase, exonuclease and endonuclease activities. Mutations in the genes recB or recC, encoding two subunits of the enzyme, reduce the frequency of many types of recombinational events. Mutations in recD, encoding the third subunit, do not reduce recombination even though most of the activities of the RecBCD enzyme are severely reduced. In this study, the genetic dependence of different types of recombination in recD mutants has been investigated. The effects of mutations in genes in the RecBCD pathway (recA and recC) as well as the genes specific for the RecF pathway (recF, recJ, recN, recO, recQ, ruv and lexA) were tested on conjugational, transductional and plasmid recombination, and on UV survival. recD mutants were hyper-recombinogenic for all the monitored recombination events, especially those involving plasmids, and all recombination events in recD strains required recA and recC. In addition, unlike recD+ strains, chromosomal recombination events and the repair of UV damage to DNA in recD strains were dependent on one RecF pathway gene, recJ. Only a subset of the tested recombination events were affected by ruv, recN, recQ, recO and lexA mutations.

Development of the hippocampal formation in mutant mice

AbstractThe highly laminated structures of the hippocampal formation provide an ideal location for the assessment of the effects of mutant genes on the development of the central nervous system. Presently seven different mutations and one genetic variant (NZB/BINJ) are known to affect the developing hippocampal formation. Each of them affects neuronal migration and/or cell proliferation in a different constellation of cell types and produces a distinct pattern of reorganization. The fact that different mutations, which map to different chromosomal locations, can affect neuronal migration in the hippocampal formation indicates that there is a variety of developmental processes that influence the ultimate destination of a migrating neuron. In addition, the fact that the different mutations do not uniformly affect all populations of migrating cells indicatesd that, in some cases, migrating neurons with different destinations may use different cues to find their final position. Conversely, the overlap in the phenotypes of the various mutations provides insight into the extent of common gene expression during neuronal migration. For example, six of the mutations have ectopic CA3 pyramidal cells. These same six mutations also have ectopic granule cells in the molecular layer of the cerebellar cortex. This association may reflect the existence of common gene expression during the migration of these two diverse cell types. Also, NZB/BINJ mice and four of the single gene mutations have immune system dysfunctions. Thus, there may be common gene expression during the differentiation of the immune system and neuronal migration. These genetic tools provide a significant new way to explore cerebral cortical development, in general, and neuronal migration, in particular.

Directional selection and variation in finite populations.

Predictions are made of the equilibrium genetic variances and responses in a metric trait under the joint effects of directional selection, mutation and linkage in a finite population. The "infinitesimal model" is analyzed as the limiting case of many mutants of very small effect, otherwise Monte Carlo simulation is used. If the effects of mutant genes on the trait are symmetrically distributed and they are unlinked, the variance of mutant effects is not an important parameter. If the distribution is skewed, unless effects or the population size is small, the proportion of mutants that have increasing effect is the critical parameter. With linkage the distribution of genotypic values in the population becomes skewed downward and the equilibrium genetic variance and response are smaller as disequilibrium becomes important. Linkage effects are greater when the mutational variance is contributed by many genes of small effect than few of large effect, and are greater when the majority of mutants increase rather than decrease the trait because genes that are of large effect or are deleterious do not segregate for long. The most likely conditions for "Muller's ratchet" are investigated.

Effect of mutant genes with a known biochemical effect on rate of formation of motor conditioned reflexes in honeybees.

1. A decrease in the speed of learning, using visual and tactile stimuli in a T maze, was demonstrated in honeybees with the chr mutation in the homozygous state in their genotype, compared with heterozygotes. 2. The inhibitory effect of the chr mutation on ability to learn is not confined to the visual sensory defect, but may be due to a biochemical shift in tryptophan metabolism, essential for activity of the nervous system of insects of this species.

Mutations affecting genetic recombination in bacteriophage T4D: II. Genetic properties

Experiments were performed to assess the effects of mutations in genes 46–47, 58, 59, w, x, and y on the correlation of genetic exchanges, on the production ofheterozygotes, and on the extent of high negative interference in bacteriophage T4D. Mutations in these genes of T4 which alter genetic recombination also alter the relative ratio of double to single crossover events and the frequency of heterozygotes for a point mutation in the rIIA cistron. In contrast, the frequency of heterozygotes for a small deletion in the rIIA cistron is essentially constant in wild-type and mutant infections. The reduction in the index of interference caused by substituting a deletion for a point mutation as the central marker in a three-factor cross is eliminated in 46 −–47 −, 59 −, w − , and y − infections.

A Pilgrim's Progress through Mutation Research

PERSPECTIVES IN BIOLOGY AND MEDICINE Volume 21 ¦ Number 3 ¦ Spring 1978 A PILGRIM'S PROGRESS THROUGH MUTATION RESEARCH C. AUERBACH* Mutations are sudden hereditary changes, as when a streptomycinresistant bacterium arises in a strain of sensitive ones and gives rise to a whole population of resistant bacteria, or when a yellow pup turns up in a kennel of black spaniels and becomes the ancestor of a line of yellow dogs. Mutation research inquires into the nature and causes of naturally occurring (spontaneous) mutations and into the means for producing mutations artificially. Mutations were objects of interest from the beginning of genetics in 1900 and had been so even earlier when they turned up as "sports" in animal or plant breeding. Mutation research as a scientific discipline was inaugurated by H. J. Müller, who, in the early 1920s, demoted mutation from its position as an unpredictable act of God to that of a chemical process that occurs rarely but at measurable rates, similar to other stochastic processes like the disintegration ofradioactive substances. The result ofa mutation is a gene with altered property and with the ability to reproduce itself. My own pilgrimage along the path of mutation "research started shortly before the Second World War when Müllerjoined our institute in Edinburgh for about a year. I had recently finished my Ph.D. thesis on a developmental problem in the fruit-fly Drosophila and was occupied with analyzing the effects ofcertain mutant genes on the development of the flies. I well remember the day when Müller came to the laboratory in which I worked, sat down beside me, and asked me what general purpose I was pursuing with my research. I answered that I wanted to find out something about the way genes act. He replied that the morphologi- *Address: Institute of Animal Genetics, University of Edinburgh, West Mains Road, Edinburgh EH9 3JN, Scotland.© 1978 by The University of Chicago. 0031-5982/78/2103-0030$01.00 Perspectives in Biology and Medicine ¦ Spring 1978 | 319 cal and histological effects of mutant genes which I was studying were still far removed from the primary action of the gene and that the best way to find out something about the gene itself was to see by which means it could be made to mutate. His enthusiasm for mutation research was infectious, and from that day on I switched to mutation research. I have never regretted it. The Basic Problem ofMutation Very early on Müller had pinpointed the fundamental mystery of mutation: the ability of a gene not only to change its properties but also to replicate at once in the changed, mutated form and to do so for hundreds of thousands or millions of times as faithfully as it had done previously in its original form [I]. In the extremely stimulating discussions which our little group around Müller had during his stay with us, the problem occupied a central place. All kinds of explanations were suggested, mainly based on analogies with physical resonance phenomena or with immunological processes. Long after Müller had gone back to the United States, the problem was solved finally and unequivocally by the Watson-Crick model ofthe gene [2]. In my experience it is rare to get a complete and final answer to a biological problem; when it does happen it is extremely satisfactory, and fortunately Müller lived to see it and to follow many of the important developments of mutation research that flowed out of it. "Molecular" geneticists often seem to think that there cannot have been any scientific study of mutation before the Watson-Crick model and that our discussions can only have been a floundering in the murky waters of speculation. They also think—and this opinion is shared by very eminent ones among them—that with this great discovery mutation research has come to an end—at least as regards its fundamental problems . Both ideas are quite wrong, as I hope to show in this article. It is true that our old discussions about the nature of self-replicating changes in the gene did not and—as I now see—could not lead to any definite conclusions without a...

Bacteria with defective rho factors suppress the effects ofN mutations in bacteriophage λ

A prediction based on the model for N-gene function of bacteriophage lambda proposed by Roberts (1971) is confirmed by showing that a lambdaN- double mutant is able to grow in strains of E. coli with defective rho transcription termination factors. The burst sizes for lambdaN- in these strains range from 5 to 24% the burst sizes for lambdaN+ in the same strain. This low level of suppression is also evident in the levels of synthesis of the lambda exonuclease and is consistent with other evidence that the defect in the rho factors of these strains is only partial. These strains do not suppress the effects of mutations in genes O, P and Q of lambda nor in genes 30 and 43 of bacteriophage T4. The lack of suppression of lambdaQ- is significant because the Q-gene product, like the N-gene product, is believed to function as an anti-terminator of lambda transcription but at termination sites that may not require rho factor action.

The role of replication proteins in the regulation of bacteriophage T4 transcription: I. Gene 45 and hydroxymethyl-C-containing DNA

In this and the following paper, expression of the phage T4 late genes in the absence of DNA replication has been examined. With only one exception, mutants that block viral replication allow synthesis of late RNA and late proteins. The peculiar character of the DNA replication-independent T4 late transcription (measured, in our experiments, as RNA that hybridizes with the isolated r-strand of T4 DNA) is the dependence of the proportion of r-transcription on the number of infecting phage and the temperature sensitivity of this transcription. Mutants in gene 45 fail to synthesize appreciable proportions of late RNA. The effects of mutations in gene 45 on late transcription are more severe than those in the other hitherto identified T4 late transcription control genes, 33 or 55. We conclude (see also the following paper by Wu et al., 1975) that the product of T4 gene 45 is required for T4 late transcription as well as for DNA replication. Mutants in four T4 DNA genes—30, 41, 46 and 56—have defective replication but synthesize some viral DNA. Mutations in three of these genes, 30, 41 and 46, allow the synthesis of T4 late RNA at levels that do not depend on the multiplicity of infection. Mutations in gene 56 (which codes for a dCTPase) lead to the synthesis of T4 DNA containing C in place of hydroxymethyl. Such DNA is subject to degradation by virus-specified endo- and exonucleases. In cells infected with a gene 56 mutant, some r-strand-specific T4 RNA is synthesized but synthesis of late T4 proteins is defective. We provide evidence that this is an intrinsic property of C-containing T4 DNA rather than a consequence of its susceptibility to degradation by phage-specified nucleases.

Effect of genotype and practice upon behavioral development in mice.

AbstractPsychomotor development from birth to 18 days of age was observed in 3 lines of mice selected for high (H), medium (M), and low (L) brain weight. Litters were cut to 8 at birth and half of the individuals randomly assigned to a practiced group tested daily; the remainder were assigned to a nonpracticed group and were tested only on selected tests on the day at which their littermates met a predesignated criterion. Significant differences between the lines were found in open field activity, balancing on a rotorod, age of eye‐opening, and edge avoidance. The H‐line was generally more advanced than either M or L. On some measures, righting for example, no strain variation was found. The effects of practice were usually significant, but did not abolish strain differences.Most research on the behavioral effects of genetic variation in the nervous system has been concerned with effects of mutant genes producing major disruption of developmental patterns. Our results indicate that genes affecting the rate and amount of normal brain growth also influence behavioral development. Genes of this type may be responsible for some of the individuality of behavioral phenotype found in natural populations.