[The role of remodeling complexes CHD1 and ISWI in spontaneous and UV-induced mutagenesis control in yeast Saccharomyces cerevisiae].

Chromatin remodulators are special multiprotein machines capable of transforming the structure, constitution, and positioning of nucleosomes on DNA. Biochemical activities of remodeling complexes CHD1 and ISWI from the SWI2/SNF2 family are well established. They ensure correct positioning of nucleosomes along the genome, which is probably critical for genome stability, in particular, after action of polymerases, repair enzymes, and transcription. In this paper, we show that single mutations in genes ISW1, ISW2, and CHD1 weakly affect repair and mutagenic processes in yeast cells. At the same time, there are differences in the effect of these mutations on spontaneous mutation levels, which indicates certain specificity of action of protein complexes ISW1, ISW2, and CHD1 on expression of different genes that control repair and mutation processes in yeast.

[Dot1 and Set2 Histone Methylases Control the Spontaneous and UV-Induced Mutagenesis Levels in the Saccharomyces cerevisiae Yeasts].

In the Saccharomyces cerevisiae yeasts, the DOT1 gene product provides methylation of lysine 79 (K79) of hi- stone H3 and the SET2 gene product provides the methylation of lysine 36 (K36) of the same histone. We determined that the dot1 and set2 mutants suppress the UV-induced mutagenesis to an equally high degree. The dot1 mutation demonstrated statistically higher sensitivity to the low doses of MMC than the wild type strain. The analysis of the interaction between the dot1 and rad52 mutations revealed a considerable level of spontaneous cell death in the double dot1 rad52 mutant. We observed strong suppression of the gamma-in- duced mutagenesis in the set2 mutant. We determined that the dot1 and set2 mutations decrease the sponta- neous mutagenesis rate in both single and d ouble mutants. The epistatic interaction between the dot1 and set2 mutations and almost similar sensitivity of the corresponding mutants to the different types of DNA damage allow one to conclude that both genes are involved in the control of the same DNA repair pathways, the ho- mologous-recombination-based and the postreplicative DNA repair.

[Control levels of Sin3 histone deacetylase for spontaneous and UV-induced mutagenesis in yeasts Saccharomyces cerevisiae].

SIN3 gene product operates as a repressor for a huge amount of genes in Saccharomyces cerevisiae. Sin3 protein with a mass of about 175 kDa is a member of the RPD3 protein complex with an assessed mass of greater than 2 million Da. It was previously shownthat RPD3 gene mutations influence recombination and repair processes in S. cerevisiae yeasts. We studied the impacts of the sin3 mutation on UV-light sensitivity and UV-induced mutagenesis in budding yeast cells. The deletion ofthe SIN3 gene causes weak UV-sensitivity of mutant budding cells as compared to the wild-type strain. These results show that the sin3 mutation decreases both spontaneous and UV-induced levels of levels. This fact is hypothetically related to themalfunction of ribonucleotide reductase activity regulation, which leads to a decrease in the dNTP pool and the inaccurate error-prone damage bypass postreplication repair pathway, which in turn provokes a reduction in the incidence of mutations.

[Interaction of gene HSM3 with genes of the epistatic RAD6 group in yeast Saccharomyces cerevisiae].

In eukaryotes, damage tolerance of matrix DNA is mainly determined by the repair pathway under the control of the RAD6 epistatic group of genes. T this pathway is also a main source of mutations generated by mutagenic factors. The results of our recent studies show that gene HSM3 participating in the control of adaptive mutagenesis increases the frequency of mutations induced by different mutagens. Mutations rad18, rev3, and mms2 controlling various stages of the RAD6 pathway are epistatic with mutation hsm3 that decreases UV-induced mutagenesis to the level typical for single radiation-sensitive mutants. The level of mutagenesis in the double mutant srs2 hsm3 was lower than in both single mutants. Note that a decrease in the level of mutagenesis relative to the single mutant srs2 depends on the mismatch repair, since this level in the triple mutant srs2 hsm3 pms 1 corresponds to that in the single mutant srs2. These data show that the mutator phenotype hsm3 is probably determined by processes occurring in a D loop. In a number of current works, the protein Hsm3 was shown to participate in the assembly of the proteasome complex S26. The assembly of proteasomes is governed by the N-terminal domain. Our results demonstrated that the Hsm3 protein contains at least two domains; the N-terminal part of the domain is responsible for the proteasome assembly, whereas the C-terminal portion of the protein is responsible for mutagenesis.

[Mutator genes of the yeast Saccharomyces cerevisiae. Interaction of mutations him and his with mutations blocking three principal pathways of repair of induced DNA damage]. / Geny-mutatory drozhzhei Saccharomyces cerevisiae. Vzaimodeistvie mutatsii him i hsm s mutatsiiami, blokiruiushchimi tri osnovnykh puti reparatsii indutsirovannykh povrezhdenii DNK.

During recent years, genes controlling mutation in higher eukaryotes have been found to be involved actively in carcinoma regeneration in cells. In this respect, studying the genetic control of mutagenesis becomes a key direction of research into mechanisms responsible for cancer generation. The results of studying interaction of mutations in the HIM and HSM genes, controlling spontaneous and induced mutagenesis in yeasts, and mutations impairing three known pathways of DNA damage repair in this microorganism, are described in this work. It was shown that mutation rev3 completely blocks UV-induced mutagenesis in all mutants studied. On the other hand, mutation rad2 synergistically interacts with mutations him1, hsm1, hsm3, hsm6, and hsm2, thus enhancing the frequency of UV-induced mutagenesis in double mutants multiple times. Mutations him2 and him3 manifested epistatic interaction with mutation rad2. With mutation rad54, the interaction was epistatic for mutations him1 and hsm2 and was additive for mutations hsm1, him2, and him3. On the basis of the data obtained, we developed a scheme for the appearance of mismatch bases in the process of repair of UV-induced DNA damage.

[Mutator genes from Saccharomyces cerevisiae. Repair of artificial heteroduplexes in him and hsm mutants]. / Geny-mutatory drozhzhei Saccharomyces cerevisiae. Reparatsiia iskusstvennykh geterodupleksov u mutantov him i hsm.

During recent years, genes controlling mutation in higher eukaryotes have been found to be involved actively in carcinoma regeneration in cells. In this respect, studying the genetic control of mutagenesis becomes a key direction of research into mechanisms responsible for cancer generation. The results of studying interaction of mutations in the HSM3 and HSM6 genes, controlling spontaneous and induced mutagenesis in yeasts, and mutations impairing three known pathways of DNA damage repair in this microorganism, are described in this work. It was shown that mutation rev3 completely blocks UV-induced mutagenesis in all mutants studied. On the other hand, mutation rad2 synergistically interacts with mutations him1, hsm1, hsm3, hsm6, and hsm2, thus enhancing the frequency of UV-induced mutagenesis in double mutants multiple times. Mutations him2 and him3 manifested epistatic interaction with mutation rad2. With mutation rad54, the interaction was epistatic for mutations him1 and hsm2 and was additive for mutations hsm1, him2, and him3. On the basis of the data obtained, we developed a scheme for the appearance of mismatch bases in the process of repair of UV-induced DNA damage.

[Mutator genes from Saccharomyces cerevisiae. Interaction between HIM- and HSM-genes]. / Geny-mutatory drozhzhei Saccharomyces cerevisiae. Vzaimodeistvie mezhdu HIM- i HSM-genami.

The interaction of six mutator genes of the yeast Saccharomyces cerevisiae with respect to UV-induced mutagenesis was studied. To this effect, double mutants with a genotype containing pairs of mutations at genes analyzed were synthesized. Analysis of the type of interaction of these mutations revealed four epistatic gene groups: (1) HIM1, HSM3, and HSM6; (2) HSM1; (3) HSM2; and (4) HIM2 and HIM3. The possible role of genes studied in different repair pathways of mispaired bases was discussed.

[Participation of the HIM1 gene from Saccharomyces cerevisiae in correction of heteroduplex DNA. Molecular cloning of the gene]. / Uchastie gena HIM1 drozhzhei Saccharomyces cerevisiae v korrektsii geterodupleksnoi DNK. Molekuliarnoe klonirovanie gena.

A group of Saccharomyces cerevisiae mutants deficient in repair of induced premutation lesions (him mutants) were previously isolated in our laboratory. Recessive him1 mutant had enhanced level of spontaneous and induced mutagenesis as well as specific altered mitotic conversion. This HIM1 gene was supposed to be involved in the process of mismatch correction of heteroduplexes. In this paper the correction efficiency of in vitro constructed heteroduplex DNA in wild-type cells and him1 mutant was studied. In the former cells heteroduplex DNA was repaired highly efficiently (about 90%), this repair efficiency being reduced in him cells approx. two times as compared with the wild-type cells. Molecular cloning of yeast chromosomal DNA fragments containing HIM1 gene was carried out. The clones were selected from the bank of yeast DNA fragments by complementing him1-1 mutation which enhances conversion frequency in ADE2 gene. One of the DNA fragments was analysed by restriction endonuclease digestion and shown to contain an insert of 6 Kb. Chromosomal integrants were obtained by homologous recombination between the plasmid and chromosomal gene him1.

[Radiation-induced instability of yeast chimeric chromosomes]. / Indutsirovannaia oblucheniem nestabil'nost' khimernykh khromosom drozhzhei.

Instability of the I chimeric chromosome of the yeast Saccharomyces induced by gamma-irradiation has been studied. The chimeric chromosome analysed contained an integrated pYF91 plasmid. Cells of the integrant were irradiated and then mated with non-irradiated cells of the proper tester strain marked by ade1 mutation (red colour of colonies). We isolated 10 hybrids with pink colonies on selective medium. They displayed high degree of mitotic instability during growth on nonselective medium, segregating red colonies (15 to 90% of the total). Tetrad analysis showed that some of the unstable chromosomes exhibited lethal effect in haploids, while others were viable and could pass through meiosis retaining their instability.