Effects of mutagen-sensitive mus mutations on spontaneous mitotic recombination in Aspergillus.

Abstract Methyl methane-sulfonate (MMS)-sensitive, radiation-induced mutants of Aspergillus were shown to define nine new DNA repair genes, musK to musS. To test mus mutations for effects on mitotic recombination, intergenic crossing over was assayed between color markers and their centromeres, and intragenic recombination between two distinguishable adE alleles. Of eight mutants analyzed, four showed significant deviations from mus+ controls in both tests. Two mutations, musK and musL, reduced recombination, while musN and musQ caused increases. In contrast, musO diploids produced significantly higher levels only for intragenic recombination. Effects were relatively small, but averages between hypo- and hyperrec mus differed 15-20-fold. In musL diploids, most of the rare color segregants resulted from mitotic malsegregation rather than intergenic crossing over. This indicates that the musL gene product is required for recombination and that DNA lesions lead to chromosome loss when it is deficient. In addition, analysis of the genotypes of intragenic (ad+) recombinants showed that the musL mutation specifically reduced single allele conversion but increased complex conversion types (especially recombinants homozygous for ad+). Similar analysis revealed differences between the effects of two hyperrec mutations; musN apparently caused high levels solely of mitotic crossing over, while musQ increased various conversion types but not reciprocal crossovers. These results suggest that mitotic gene conversion and crossing over, while generally associated, are affected differentially in some of the mus strains of Aspergillus nidulans.

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Isolation and characterization of Schizosaccharomyces pombe mutants affected in mitotic recombination.

Genetics ◽

10.1093/genetics/128.3.495 ◽

1991 ◽

Vol 128 (3) ◽

pp. 495-504

Author(s):

A Gysler-Junker ◽

Z Bodi ◽

J Kohli

Keyword(s):

Schizosaccharomyces Pombe ◽

Mitotic Recombination ◽

Selective Medium ◽

Intragenic Recombination ◽

Crossing Over ◽

Wild Type ◽

Isolation And Characterization ◽

Mitotic Gene Conversion ◽

Type Frequency

Abstract A haploid Schizosaccharomyces pombe strain carrying a heteroallelic duplication of the ade6 gene was used to isolate mitotic recombination-deficient mutants. Recombination between the different copies of the ade6 gene can lead to Ade+ segregants. These are observed as growing papillae when colonies of a suitable size are replicated onto selective medium. We isolated mutants which show an altered papillation phenotype. With two exceptions, they exhibit a decrease in the frequency of mitotic recombination between the heteroalleles of the duplication. The two other mutants display a hyper-recombination phenotype. The 12 mutations were allocated to at least nine distinct loci by recombination tests. Of the eight rec mutants analyzed further, six were also affected in mitotic intergenic recombination in the intervals cen2-mat or cen3-arg 1. No effect on mitotic intragenic recombination was observed. These data suggest that mitotic gene conversion and crossing over can be separated mutationally. Meiotic recombination occurs at the wild-type frequency in all mutants investigated.

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Spontaneous mitotic recombination in yeast: the hyper-recombinational rem1 mutations are alleles of the RAD3 gene.

Genetics ◽

10.1093/genetics/119.2.289 ◽

1988 ◽

Vol 119 (2) ◽

pp. 289-301

Author(s):

B A Montelone ◽

M F Hoekstra ◽

R E Malone

Keyword(s):

Saccharomyces Cerevisiae ◽

Gene Conversion ◽

Excision Repair ◽

Mitotic Recombination ◽

Crossing Over ◽

Wild Type ◽

Recombination Repair ◽

Mitotic Gene Conversion ◽

Type Gene ◽

Repair Genes

Abstract The RAD3 gene of Saccharomyces cerevisiae is required for UV excision-repair and is essential for cell viability. We have identified the rem1 mutations (enhanced spontaneous mitotic recombination and mutation) of Saccharomyces cerevisiae as alleles of RAD3 by genetic mapping, complementation with the cloned wild-type gene, and DNA hybridization. The high levels of spontaneous mitotic gene conversion, crossing over, and mutation conferred upon cells by the rem1 mutations are distinct from the effects of all other alleles of RAD3. We present preliminary data on the localization of the rem1 mutations within the RAD3 gene. The interaction of the rem1 mutant alleles with a number of radiation-sensitive mutations is also different than the interactions reported for previously described (UV-sensitive) alleles of RAD3. Double mutants of rem1 and a defect in the recombination-repair pathway are inviable, while double mutants containing UV-sensitive alleles of RAD3 are viable. The data presented here demonstrate that: (1) rem1 strains containing additional mutations in other excision-repair genes do not exhibit elevated gene conversion; (2) triple mutants containing rem1 and mutations in both excision-repair and recombination-repair are viable; (3) such triple mutants containing rad52 have reduced levels of gene conversion but wild-type frequencies of crossing over. We have interpreted these observations in a model to explain the effects of rem1. Consistent with the predictions of the model, we find that the size of DNA from rem1 strains, as measured by neutral sucrose gradients, is smaller than wild type.

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RAD52-INDEPENDENT MITOTIC GENE CONVERSION IN SACCHAROMYCES CEREVISIAE FREQUENTLY RESULTS IN CHROMOSOMAL LOSS

Genetics ◽

10.1093/genetics/111.1.7 ◽

1985 ◽

Vol 111 (1) ◽

pp. 7-22

Author(s):

James E Haber ◽

Mark Hearn

Keyword(s):

Saccharomyces Cerevisiae ◽

Gene Conversion ◽

Mitotic Recombination ◽

Gene Conversion Event ◽

Intragenic Recombination ◽

Wild Type ◽

Conversion Event ◽

Chromosomal Loss ◽

Mitotic Gene Conversion ◽

Striking Effect

ABSTRACT We have examined spontaneous, interchromosomal mitotic recombination events between his4 alleles in both Rad+ and rad52 strains of Saccharomyces cerevisiae. In Rad+ strains, 74% of the His+ prototrophs resulted from gene conversion events without exchange of flanking markers. In diploids homozygous for the rad52-1 mutation, the frequency of His+ prototroph formation was less than 5% of the wild-type value, and more than 80% of the gene conversion events were accompanied by an exchange of flanking markers. Most of the rad52 intragenic recombination events arose by gene conversion accompanied by an exchange of flanking markers and not by a simple reciprocal exchange between the his4A and his4C alleles. There were also profound effects on the kinds of recombinant products that were recovered. The most striking effect was that RAD52-independent mitotic recombination frequently results in the loss of one of the two chromosomes participating in the gene conversion event.

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Increased intragenic recombination and non-disjunction in the Rec-1 strain of Caenorhabditis elegans

Genetics Research ◽

10.1017/s0016672300024095 ◽

1988 ◽

Vol 51 (2) ◽

pp. 89-93 ◽

Cited By ~ 3

Author(s):

B. Rattray ◽

A. M. Rose

Keyword(s):

Caenorhabditis Elegans ◽

Gene Conversion ◽

Recombination Frequency ◽

Spontaneous Mutation ◽

Selective Advantage ◽

Dna Lesions ◽

Intragenic Recombination ◽

Crossing Over ◽

Spontaneous Mutation Rate ◽

Independent Events

SummaryThe Rec-1 strain of Caenorhabditis elegans increases recombination frequency three-fold. In this paper, we have investigated the effect of Rec-1 on the intragenic recombination phenomena of crossing-over and gene conversion. These events were increased two- to three-fold as was X-chromosome non-disjunction. All of the recovered recombinants were independent events, indicating that Rec-1 does not act pre-meiotically. The pattern of recombination in the Rec-1 strain resembles a meiotic pattern more than a radiation expansion. We conclude from this result that the Rec-1 enhancement of recombination is not the result of an increased number of DNA lesions randomly distributed along the chromosome. The increased recombination frequency of Rec-1 was not accompanied by any detrimental effects on growth, progeny number or spontaneous mutation rate. In this regard, the results may have implications for models which propose either selective advantage or disadvantage accompanying increased recombination.

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Crossing Over Is Rarely Associated With Mitotic Intragenic Recombination in Schizosaccharomyces pombe

Genetics ◽

10.1093/genetics/157.1.63 ◽

2001 ◽

Vol 157 (1) ◽

pp. 63-77 ◽

Cited By ~ 2

Author(s):

Jeffrey B Virgin ◽

Jeffrey P Bailey ◽

Farnaz Hasteh ◽

James Neville ◽

Amy Cole ◽

...

Keyword(s):

Schizosaccharomyces Pombe ◽

Chromosomal Rearrangements ◽

Mitotic Recombination ◽

Intragenic Recombination ◽

Crossing Over ◽

Recombination Rates ◽

Alternative Pathways ◽

Ectopic Recombination ◽

Specific Factors ◽

Differential Control

Abstract Chromosomal rearrangements can result from crossing over during ectopic homologous recombination between dispersed repetitive DNA. We have previously shown that meiotic ectopic recombination between artificially dispersed ade6 heteroalleles in the fission yeast Schizosaccharomyces pombe frequently results in chromosomal rearrangements. The same recombination substrates have been studied in mitotic recombination. Ectopic recombination rates in haploids were ∼1-4 × 10-6 recombinants per cell generation, similar to allelic recombination rates in diploids. In contrast, ectopic recombination rates in heterozygous diploids were 2.5-70 times lower than allelic recombination or ectopic recombination in haploids. These results suggest that diploid-specific factors inhibit ectopic recombination. Very few crossovers occurred in ade6 mitotic recombination, either allelic or ectopic. Allelic intragenic recombination was associated with 2% crossing over, and ectopic recombination between multiple different pairing partners showed 1-7% crossing over. These results contrast sharply with the 35-65% crossovers associated with meiotic ade6 recombination and suggest either differential control of resolution of recombination intermediates or alternative pathways of recombination in mitosis and meiosis.

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Induced rates of mitotic crossing over and possible mitotic gene conversion per wing anlage cell in Drosophila melanogaster by X rays and fission neutrons.

Genetics ◽

10.1093/genetics/126.1.157 ◽

1990 ◽

Vol 126 (1) ◽

pp. 157-166 ◽

Cited By ~ 1

Author(s):

T Ayaki ◽

K Fujikawa ◽

H Ryo ◽

T Itoh ◽

S Kondo

Keyword(s):

Drosophila Melanogaster ◽

Gene Conversion ◽

Mitotic Recombination ◽

X Rays ◽

Strand Breaks ◽

Order Of Magnitude ◽

Radiation Induced ◽

Secondary Result ◽

Mitotic Gene Conversion ◽

Fission Neutrons

Abstract As a model for chromosome aberrations, radiation-induced mitotic recombination of mwh and flr genes in Drosophila melanogaster strain (mwh +/+ flr) was quantitatively studied. Fission neutrons were five to six times more effective than X rays per unit dose in producing either crossover-mwh/flr twins and mwh singles-or flr singles, indicating that common processes are involved in the production of crossover and flr singles. The X-ray-induced rate/wing anlage cell/Gy for flr singles was 1 X 10(-5), whereas that of crossover was 2 x 10(-4); the former and the latter rate are of the same order of magnitude as those of gene conversion and crossover in yeast, respectively. Thus, we conclude that proximal-marker "flr" singles induced in the transheterozygote are gene convertants. Using the model based on yeast that recombination events result from repair of double-strand breaks or gaps, we propose that mitotic recombination in the fly is a secondary result of recombinational DNA repair. Evidence for recombinational misrepair in the fly is given. The relative ratio of radiation-induced mitotic crossover to spontaneous meiotic crossover is one order of magnitude higher in the fly than in yeast and humans.

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Immunomodulatory Effects of Radiotherapy

International Journal of Molecular Sciences ◽

10.3390/ijms21218151 ◽

2020 ◽

Vol 21 (21) ◽

pp. 8151

Author(s):

Sharda Kumari ◽

Shibani Mukherjee ◽

Debapriya Sinha ◽

Salim Abdisalaam ◽

Sunil Krishnan ◽

...

Keyword(s):

Molecular Mechanisms ◽

Carbon Particle ◽

Dna Lesions ◽

X Rays ◽

Adaptive Immune ◽

High Let Radiation ◽

Different Types ◽

High Let ◽

Radiation Induced ◽

Tumor Death

Radiation therapy (RT), an integral component of curative treatment for many malignancies, can be administered via an increasing array of techniques. In this review, we summarize the properties and application of different types of RT, specifically, conventional therapy with x-rays, stereotactic body RT, and proton and carbon particle therapies. We highlight how low-linear energy transfer (LET) radiation induces simple DNA lesions that are efficiently repaired by cells, whereas high-LET radiation causes complex DNA lesions that are difficult to repair and that ultimately enhance cancer cell killing. Additionally, we discuss the immunogenicity of radiation-induced tumor death, elucidate the molecular mechanisms by which radiation mounts innate and adaptive immune responses and explore strategies by which we can increase the efficacy of these mechanisms. Understanding the mechanisms by which RT modulates immune signaling and the key players involved in modulating the RT-mediated immune response will help to improve therapeutic efficacy and to identify novel immunomodulatory drugs that will benefit cancer patients undergoing targeted RT.

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Coexistence of SOS-Dependent and SOS-Independent Regulation of DNA Repair Genes in Radiation-Resistant Deinococcus Bacteria

Cells ◽

10.3390/cells10040924 ◽

2021 ◽

Vol 10 (4) ◽

pp. 924

Author(s):

Laurence Blanchard ◽

Arjan de Groot

Keyword(s):

Dna Repair ◽

Deinococcus Radiodurans ◽

Dna Repair Genes ◽

Lesion Bypass ◽

Radiation Resistant ◽

Radiation Induced ◽

Induced Mutagenesis ◽

High Doses ◽

Translesion Polymerases ◽

Repair Genes

Deinococcus bacteria are extremely resistant to radiation and able to repair a shattered genome in an essentially error-free manner after exposure to high doses of radiation or prolonged desiccation. An efficient, SOS-independent response mechanism to induce various DNA repair genes such as recA is essential for radiation resistance. This pathway, called radiation/desiccation response, is controlled by metallopeptidase IrrE and repressor DdrO that are highly conserved in Deinococcus. Among various Deinococcus species, Deinococcus radiodurans has been studied most extensively. Its genome encodes classical DNA repair proteins for error-free repair but no error-prone translesion DNA polymerases, which may suggest that absence of mutagenic lesion bypass is crucial for error-free repair of massive DNA damage. However, many other radiation-resistant Deinococcus species do possess translesion polymerases, and radiation-induced mutagenesis has been demonstrated. At least dozens of Deinococcus species contain a mutagenesis cassette, and some even two cassettes, encoding error-prone translesion polymerase DnaE2 and two other proteins, ImuY and ImuB-C, that are probable accessory factors required for DnaE2 activity. Expression of this mutagenesis cassette is under control of the SOS regulators RecA and LexA. In this paper, we review both the RecA/LexA-controlled mutagenesis and the IrrE/DdrO-controlled radiation/desiccation response in Deinococcus.

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Regulation of Mitotic Homeologous Recombination in Yeast: Functions of Mismatch Repair and Nucleotide Excision Repair Genes

Genetics ◽

10.1093/genetics/154.1.133 ◽

2000 ◽

Vol 154 (1) ◽

pp. 133-146 ◽

Cited By ~ 1

Author(s):

Ainsley Nicholson ◽

Miyono Hendrix ◽

Sue Jinks-Robertson ◽

Gray F Crouse

Keyword(s):

Saccharomyces Cerevisiae ◽

Mismatch Repair ◽

Nucleotide Excision Repair ◽

Excision Repair ◽

Mitotic Recombination ◽

Inverted Repeats ◽

Replication Errors ◽

Nucleotide Excision ◽

Homeologous Recombination ◽

Repair Genes

Abstract The Saccharomyces cerevisiae homologs of the bacterial mismatch repair proteins MutS and MutL correct replication errors and prevent recombination between homeologous (nonidentical) sequences. Previously, we demonstrated that Msh2p, Msh3p, and Pms1p regulate recombination between 91% identical inverted repeats, and here use the same substrates to show that Mlh1p and Msh6p have important antirecombination roles. In addition, substrates containing defined types of mismatches (base-base mismatches; 1-, 4-, or 12-nt insertion/deletion loops; or 18-nt palindromes) were used to examine recognition of these mismatches in mitotic recombination intermediates. Msh2p was required for recognition of all types of mismatches, whereas Msh6p recognized only base-base mismatches and 1-nt insertion/deletion loops. Msh3p was involved in recognition of the palindrome and all loops, but also had an unexpected antirecombination role when the potential heteroduplex contained only base-base mismatches. In contrast to their similar antimutator roles, Pms1p consistently inhibited recombination to a lesser degree than did Msh2p. In addition to the yeast MutS and MutL homologs, the exonuclease Exo1p and the nucleotide excision repair proteins Rad1p and Rad10p were found to have roles in inhibiting recombination between mismatched substrates.

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ALTERED FIDELITY OF MITOTIC CHROMOSOME TRANSMISSION IN CELL CYCLE MUTANTS OF S. CEREVISIAE

Genetics ◽

10.1093/genetics/110.3.381 ◽

1985 ◽

Vol 110 (3) ◽

pp. 381-395

Author(s):

Leland H Hartwell ◽

David Smith

Keyword(s):

Cell Cycle ◽

Gene Product ◽

Mitotic Chromosome ◽

Mitotic Recombination ◽

Chromosome Loss ◽

Temperature Sensitive ◽

Repair Pathway ◽

Dna Metabolism ◽

Temperature Sensitive Mutants ◽

Chromosome Transmission

ABSTRACT Thirteen of 14 temperature-sensitive mutants deficient in successive steps of mitotic chromosome transmission (cdc2, 4, 5, 6, 7, 8, 9, 13, 14, 15, 16, 17 and 20) from spindle pole body separation to a late stage of nuclear division exhibited a dramatic increase in the frequency of chromosome loss and/or mitotic recombination when they were grown at their maximum permissive temperatures. The increase in chromosome loss and/or recombination is likely to be due to the deficiency of functional gene product rather than to an aberrant function of the mutant gene product since the mutant alleles are, with one exception, recessive to the wild-type allele for this phenotype. The generality of this result suggests that a delay in almost any stage of chromosome replication or segregation leads to a decrease in the fidelity of mitotic chromosome transmission. In contrast, temperature-sensitive mutants defective in the control step of the cell cycle (cdc28), in cytokinesis (cdc3) or in protein synthesis (ils1) did not exhibit increased recombination or chromosome loss.—Based upon previous results with mutants and DNA-damaging agents in a variety of organisms, we suggest that the induction of mitotic recombination in certain mutants is due to the action of a repair pathway upon nicks or gaps left in the DNA. This interpretation is supported by the fact that the induced recombination is dependent upon the RAD52 gene product, an essential component in the recombinogenic DNA repair pathway. Gene products whose deficiency leads to induced recombination are, therefore, strong candidates for proteins that function in DNA metabolism. Among the mutants that induce recombination are those known to be defective in some aspect of DNA replication (cdc2, 6, 8, 9) as well as some mutants defective in the G2 (cdc13 and 17) and M (cdc5 and 14) phases of the mitotic cycle. We suggest that special aspects of DNA metabolism may be occurring in G2 and M in order to prepare the chromosomes for proper segregation.

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