[clpP2 gene encoding peptidase in cyanobacteria Synechocystis sp. PCC 6803 controls the sensitivity of cells to photoinhibition]. / Gen clpP2, kodiruiushchii peptidazu u tsianobakterii Synechocystis sp. PCC 6803, kontroliruet chuvstvitel'nost' kletok k fotoingibirovaniiu.

A homozygous insertion mutant with the inactivated clpP2 gene, which encodes the proteolytic subunit of ATP-dependent peptidase, was obtained in the unicellular cyanobacterium Synechocystis sp. PCC 6803. The mutant cannot grow under photoautotrophic conditions, but cells grown under heterotrophic conditions in a glucose-containing medium have active photosystems I and II (PS I and PS II). The loss of capacity for photoautotrophic growth is determined by a high sensitivity of mutant cells to the inactivating effect of light. Their incubation under light with an intensity above 10 microE m-2 s-1 inhibits cell growth in culture and causes degradation of photosynthetic pigments. It is proposed that the ClpP2 peptidase is involved in the protection of Synechocystis 6803 cells from photoinhibition.

[Repair of dual-stranded DNA in Saccharomyces cerevisiae cells: homolog-dependent ligation and role of the RAD55 gene]. / Reparatsiia dvunitevykh breshei DNK v kletkakh Saccharomyces cerevisiae: gomolog-zavisimoe ligirovanie i rol' gena RAD55.

In our previous works, a mutation in the RAD57 gene was shown to induce the plasmid DNA double-strand gap (DSG) repair via a special recombinational repair mechanism: homolog-dependent ligation responsible for reuniting disrupted plasmid ends without reconstructing the sequence lost because of the DSG. In this work, the role of the RAD55 gene in the plasmid DNA DSG repair was studied. A cold-sensitive rad55-3 mutation markedly decreased the precision of plasmid DNA DSG repair under conditions of restrictive temperature (23 degrees C): only 5-7% of plasmids can repair DSG, whereas under permissive conditions (36 degrees C), DSGs were repaired in approximately 50% of the cells. In the cold-sensitive mutation rad57-1, the proportion of plasmids in which DSGs were repaired was nearly the same under both permissive and restrictive conditions (5-10%). The results indicate that a disturbance in the function of the RAD55 gene, as in the RAD57 gene, leads to a drastic increase in the contribution of homolog-dependent ligation to the repair of double-strand DNA breaks.

[Molecular-genetic analysis of dual-stranded DNA break repair in saccharomyces yeasts]. / Molekuliarno-geneticheskii analiz reparatsii dvunitevykh razryvov DNK u drozhzhei sakharomitsetov.

DNA double-strand breaks (DSB) are the most dangerous damage to genetic material caused by ionizing radiation and some chemical agents. Nonrestored DSB lead to chromosomal rearrangements, genetic instability, and cell death. On the other hand, DSB normally occur in cells in the course of normal gene functioning. DSB repair not only protects cells from adverse consequences and maintains stability of genetic material but is directly involved in the most important processes of cell life, such as meiosis and humoral immunity in vertebrates. The diverse mechanisms of homologous and nonhomologous recombination underlie DSB repair. In this respect, yeast are the best-studied object. In this review, genetic control and molecular models of the recombination DNA DSB repair in Saccharomyces cerevisiae are considered. Evidence has accumulated that indicates the higher eukaryotes retained the basic set of the repair pathways characteristic of bacteria and lower eukaryotes. However, different repair mechanisms predominate in yeast as compared to higher eukaryotes. Therefore, the results obtained in yeast experiments may be applicable to higher eukaryotes.

[Role of the RAD57 gene in the repair of double-stranded DNA gaps in the yeast Saccharomyces cerevisiae]. / Roli gena RAD57 v reparatsii dvunitevykh breshei DNK u drozhzhei Saccharomyces cerevisiae.

The linearized plasmid with complementary (cohesive) ends was shown to restore the circular form in cells of the rad57 mutant with a lower efficiency than in Rad+ cells. This process proved to be cold-sensitive in mutant cells, in contrast to wild-type cells. When mutant cells were shifted from 23 up to 36 degrees C, the repair efficiency increased approximately 1.5 times. In most cases examined, the repair was not accompanied by the doublestrand gap repair within the break site and did not depend on temperature. Homology between chromosomal and plasmid DNA sequences in the break region and the presence of cohesive ends were shown to be essential for the repair of linearized plasmids with a double-strand gap in cells of the rad57 mutant. Degradation of cohesive ends of the linearized plasmid during its repair in rad57 cells is insignificant. Possible mechanisms of linearized plasmid repair in the rad57 mutant are proposed.

[Cloning and identification of the gene controlling nitrogen metabolism in the photosynthetic purple bacteria Rhodobacter sphaeroides]. / Klonirovanie i identifikatsiia gena, kontroliruiushchego azotistyi metabolizm u fotosinteziruiushchei purpurnoi bakterii Rhodobacter sphaeroides.

A recombinant plasmid has been selected from the genomic library of Rhodobacter sphaeroides that restores the properties of the wild type strain in the mutant Drn121. The latter possesses the derepressed synthesis of nitrogenase when grown in the light, inability of nitrogen fixation in the dark and growth on potassium nitrate as a single source of nitrogen, disruption of ammonium ions and methylamine transportation, decreased activity of glutamine synthetase. The gene complementing the drn121 mutation is localized within the EcoRI-HindIII fragment of Rhodobacter sphaeroides chromosome 2.25 kb in size. Analysis of the fragment nucleotide sequence has revealed the fragments with a high level of homology to regulatory genes ntrB (the 3'-end) and ntrC of Rhodobacter capsulatus. The plasmid pRCN102, containing the nifR3-ntrB-ntrC operon of Rhodobacter capsulatus, is able to complement the drn121 mutation while its derivatives having inactivated ntrN or ntrC genes are not. Hence, in Rhodobacter sphaeroides mutant Drn121 the mutation is localized in ntrC gene the product of which is involved not only in nitrogen fixation but also in nitrogen metabolism on the whole.

[Genetic instability of colonies' morphologic characteristics in the yeast Saccharomyces cerevisiae. The influence of mutations of radiosensitivity]. / Geneticheskaia nestabil'nost' po priznaky morfologii kolonii u drozhzhei Saccharomyces cerevisiae. Vliianie mutatsii radiochuvstvitel'nosti.

The exposure to ionizing radiation of radiosensitive mutants of diploid yeast Saccharomyces cerevisiae deficient in double-strand break repair results in formation of morphologically unstable colonies. Some characteristics of this process were studied. The results obtained are consistent with the hypothesis on relationship between DNA double-strand breaks or their repair with the formation of unstable clones of diploid yeast cells.

[An evaluation in the Ames test of the mutagenicity of the sewage and industrial effluents from the Baikal Paper and Pulp Combine]. / Otsenka na mutagennost' v teste Eimsa stochnykh vod i proizvodstvennykh potokov Baikal'skogo tselliulozno-bumazhnogo kombinata.

The use of the Ames test for the analysis of industrial effluents from cellulose production and sewage waters varying in the degree of purification with the aid of a metabolic activation system from rat and fish liver with Salmonella strains TA 98 and TA 100 revealed a strong direct mutagenic effect of strain TA 100 in samples after cellulose chlorination. The multistage procedure of sewage water purification allows to remove practically completely the mutagenic substances. A simultaneous study of cytotoxic effects of industrial effluents on mammalian cells shows that the mutagenic activity is exhibited in not toxic concentrations. The urgency of a regular biological control over the genotoxicity of industrial effluents from the sulfate production of cellulose is under discussion.

[Repair of a double-stranded gap in plasmid DNA in radiosensitive mutants of Saccharomyces cerevisiae: effectiveness and precision]. / Reparatsiia dvunitevykh breshei plazmidnoi DNK u radiochuvstvitel'nykh mutantov Saccharomyces cerevisiae: éffektivnost' i tochnost'.

The repair of a double strand gap in plasmid DNA in radiosensitive mutants of Saccharomyces cerevisiae has been studied. The proportion of repair events resulting in the complete doublestrand gap recovery of the plasmid DNA has been found to be close to 100% in Rad+ cells. The mutation rad55 did not interfere in the doublestrand gap repair efficiency and accuracy. The mutant rad57 is capable of the effective doublestrand gap repair without restoration of the DNA sequence deleted by the gap. The mutation rad53 substantially inhibited the efficiency of the doublestrand gap repair but did not influence the accuracy of the repair. Plasmid DNA doublestranded gap repair is completely blocked by mutations rad50 and rad54.

[A model system for the study of repair of DNA double-strand breaks in Saccharomyces cerevisiae]. / Model'naia sistema dlia izucheniia reparatsii dvunitevykh razryvov DNK u drozhzhei Saccharomyces cerevisiae.

The efficiency of "LiCl transformation" in Saccharomyces cerevisiae haploid cells by an autonomously replicating pLL12 plasmid carrying yeast LEU2 and LYS2 genes is increased (by an order or more) when the plasmid is linearized by the restriction endonuclease XhoI cleavage of a unique site in LYS2 gene. Transformants were selected on the medium lacking leucine. This phenomenon has been shown to be a result of recombinational repair of double-strand breaks (DSB) of plasmid DNA stimulated by a restriction endonuclease. The kinetic data have shown the process of plasmid DNA DSB repair to consist of two phases. The completion of the first phase occurs during an hour and the second phase occurs in 14-18 hours. DNA double-strand gaps (the deleted sequences of plasmid LYS2 gene in DSB region) with maximal length of 2-2.5 kb are repaired with the same efficiency as DSB. The genetic control of the recombinational repair of plasmid DNA DSB has been studied.

[Mutability of the LYS2 gene in diploid saccharomycete yeasts. I. The occurrence of spontaneous mutants and mutants induced by x-ray and ultraviolet radiation]. / Izuchenie mutabil'nosti gena LYS2 u diploidov drozhzhei sakharomitsetov. Soobshchenie I. Vozniknovenie spontannykh mutantov i mutantov, indutsirovannykh rentgenovskim i ul'trafioletovym izlucheniem.

More than 3000 spontaneous and induced lys2 mutants were obtained in haploid and diploid strains of yeast Saccharomyces. The ability to utilize alpha-aminoadipate was used for lys2 mutant screening. The spontaneous and induced mutation rates were measured in haploid and diploid strains. Mitotic segregation of pho1 marker linked to LYS2 was studied in lys2 mutants obtained in diploid strains. Fertility of diploid lys2 mutants was tested. The conclusion to be drawn from the data presented is that mutations appeared in one of two homologous chromosomes and then segregated by mitotic homozygotization.

[Test systems for biomonitoring based on membrane-bound enzyme complexes. V. Mixed-function monooxygenase induction in the liver microsomes of Lake Baikal fish]. / Test-sistemy dlia biomonitoringa na osnove membranno-sviazannykh ferment nykh kompleksov. V. Induktsiia monooksigenaz so smeshannoi funktsiei v mikrosomakh pecheni baikal'skikh ryb.

The content of cytochrome P450 and monooxygenase activity has been studied in the liver of Baikal fishes (Coregonus automnalis, Thymallus articus, Brachymystax lenok and Cottocomphorus greminsky). The administration of 3-methylcholanthrene increases considerably the level of metabolic activity of microsomal fraction and cytochrome P450 content in liver. The data of microsomal fractions of rats and fishes liver electrophoresis have shown that xenobiotic causes the synthesis of similar according to the molecular weight forms of cytochrome P450 in these animals. The induction of microsomal monooxygenase inhibits the lipid peroxidation of microsomal fraction.

[Test systems for biomonitoring based on membrane-bound enzyme complexes. IV. Assessment of genotoxic effects in an Ames test system with metabolic activation by the microsomal mono-oxygenases from fish livers]. / Test-sistemy dlia biomonitoringa na osnove membranno-sviazannykh fermentnykh kompleksov. IV. Otsenka genotokischeskikh éffektov v testsisteme Eimsa s metabolicheskoi aktivatsiei mikrosomal'nymi monooksigenazami iz pecheni ryb.

The study of mutagenic effect of 2-aminoantracene and benz(alpha)pyrene on Salmonella triphimurium TA 100 in the Ames test-system in the presence of postmitochondrial fractions S-9 from carp liver with 3-methylcholantrene induced by microsomal oxidation system has been carried out. The metabolic activity and cytochrome P450 contence in carp liver microsomes have been shown to concede considerably those in rats liver. But these characteristics are sufficient for the use of fraction S-9 from carp liver for the study of genotoxic effect of these xenobiotics in the Ames test-system. Several regimes of storage of S-9 preparations from carp liver have been compared. S-9 preparations frozen immediately after isolation preserve their metabolic activity with respect to 2-aminoantracene and benz(alpha)pyrene well.

Mitotic intragenic recombination in the yeast Saccharomyces: marker-effects on conversion and reciprocity of recombination.

We have made a large scale analysis of prototrophic products of spontaneous and induced mitotic recombination within LYS2 gene of the yeast Saccharomyces. The mutant alleles staying in heterozygote with the wild type allele were uncovered and analysed.Among thirteen lys2 mutations used in the study three had reduced frequencies of mitotic gene conversion. These rarely converting mutations gave a remarkably high proportion of reciprocal events (up to 38%) in pairwise combinations, never seen for any other pair of alleles studied. Two of these mutations are the deletions of large parts of LYS2 gene.The results suggest that mispairing in the region of deletion blocks the hybrid DNA migration and leads to the reduced conversion ability of deletions. Comparison of uncovered alleles ratio in all allele combinations tested lead us to another hypothesis about bidirectional migration of hybrid DNA.

[Test-systems for biomonitoring based on membrane-bound enzyme complexes. III. An assessment of the genotoxic action of industrial effluents in the Ames test-system with metabolic activation by microsomal monooxygenases]. / Test-sistemy dlia biomonitoringa na osnove membranno-sviazannykh fermentnykh kompleksov. III. Otsenka genotokischeskogo deistviia promyshlennykh stokov v test-sisteme Eimsa s metabolicheskoi aktivatsiei mikrosomal'nymi monooksigenazami.

Using the Ames mutation test system II samples of the Baikal pulp and paper effluents selected at different dates have been investigated. In 9 cases the effluent samples possessed no mutagenic activity; some samples revealed frame shift mutations, i.e. a medium mutagenic effect. In the presence of a metabolic activation system from the livers of phenobarbital-induced rats the mutagenic activity was considerably reduced.