[The regularities of the induction of DNA double strand breaks and DNA repair in human lymphocytes after irradiation by accelerated heavy ions with different energy].

The regularities of the induction of DNA double strand breaks (DSB) in human lymphocytes after irradiation by different doses of accelerated lithium and carbon ions (33 and 480 MeV/nucleon, LET = 20 and 10.6 keV/microm, respectively) and gamma-rays 60Co by using of comet assay were investigated. It was shown that the dependence of DSB formation increases linearly with growing of the dose of lithium and carbon ions and gamma-rays. The biological effectiveness of carbon ions with high energy was similar with gamma-rays, lithium ions possess greater biological effectiveness in comparison with gamma-rays and value of RBE of lithium ions amount 1.6 +/- 0.1. The kinetic of DNA repair from DSB in human lymphocytes after irradiation by lithium and carbon ions and gamma-rays was studied. It is revealed that the reparation proceeds effectively with heavy ion and gamma-ray irradiation by exponential kinetics.

[Induction of gene and deletion mutations by accelerated heavy charged particles in Escherichia coli cells].

The results of the induction of the point and the deletion mutations by the radiation with broad region of linear energy transfer (LET) ox Escherichia coli cells. The linear-quadratic function for point mutation induction was shown in comparison with linear dependence for deletion mutations. The relative biological effectiveness (RBE) is described as a function of LET by dependence with a local maximum. The greatest RBE coefficients for the lethal effects, gene and deletion mutation induction realize under different LET of heavy charged particles.

[Regularities of excising transposon Tn10 in rec-mutant E. coli cells exposed to gamma radiation]. / Zakonomernosti ékstsizii transpozona Tn10 v kletkakh rec-mutantov E. coli pri gamma-obluchenii.

The regularities of gamma-induced excision of transposon Tn10 in different rec-strains of E. coli cells after gamma-irradiation have been studied. The survival of cells and relative frequency of the Tn10 elimination as a function of the 137Cs gamma-radiation doses were investigated. RecN and recA-mutants of E. coli were used for study of the role of rec-genes in the gamma-induced transposon excision. It was shown that the induced excision in the recN mutant was reduced. The transposon excision in the recA mutant was not revealed. The obtained results let to conclude that recA, and recN genes are involved not only in DNA repair processes but also in the gamma-induced transposon excision in bacteria.

[The patterns of the mutagenic action of radiations with different LETs on Bacillus subtilis cells]. / Zakonomernosti mutagennogo deistviia izluchenii s raznoi LPE na kletki Bacillus subtilis.

The induction of the his(-)-->his+ mutants in vegetative and spores of Bacillus subtilis wild-type cells irradiated with gamma rays and helium ions (LET = 20-80 keV/micron) has been investigated. It was shown that the dose dependence of the mutation induction in vegetative cells is described by a linear-quadratic function of dose in case of both gamma-rays and helium ions. RBE (LET) dependencies on the lethal and mutagenic effect of irradiation have a local maximum. The maximum of RBE (LET) dependence on the mutagenic assay is shifted at the low region of LET in comparison with the lethal effect of irradiation.

[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.

[Relative competitiveness of haploid and diploid yeast cells growing in a mixed population]. / Otnositel'naia konkurentnosposobnost' gaploidnykh i diploidnykh drozhzhevykh kletok pri roste v smeshannoi populiatsii.

Saccharomyces cerevisiae was grown in a rich medium under the conditions of "quasi-continuous" cultivation and, after 200-300 generations, its diploid cells almost completely displaced haploid cells from the original mixed "haploid-diploid" population where the ratio between diploid and haploid strains was either 1:1 or 1:100. The cultivation at 40 degrees C did not change the relative competitive ability of haploids and diploids. When cells were cultivated in a rich medium at 6 degrees C or in a minimal medium at 30 degrees C, none of the strains showed an advantage over others for about 200 generations. Haploid cells had an advantage over diploid cells during "quasi-continuous" growth in the minimal medium at 30 degrees C. When the temperature was elevated to 40 degrees C, diploid cells displaced haploid cells from the mixed population. No advantage was found for diploid or haploid cells grown in a medium with an elevated KCl content (1.5 M). Haploid cells had an advantage over diploid cells when Pichia pinus was cultivated in a minimal medium. The results are discussed using the hypothesis about the diploid phase being fixed in the course of biological evolution.

[Regularities of posthyperthermic recovery in haploid and diploid yeasts Saccharomyces cerevisiae and Pichia pinus]. / Zakonomernosti postgipertermicheskogo vosstanovleniia u gaploidnykh i diploidnykh drozhzhei Saccharomyces cerevisiae i Pichia pinus.

Isogenic diploid cells of Saccharomyces cerevisiae are more sensitive to hyperthermic treatment (50 degrees C) than haploid ones, the posthyperthermical recovery efficiency being the same for both the cell types. In contrast to this, thermosensitivity of haploid and diploid cells of Pichia pinus does not practically differ, the posthyperthermic recovery efficiency for both the cell types being also the same. It is shown that diploid cells of P. pinus in the logarithmic phase of their growth are incapable of recovering after hyperthermal treatment, which is largely the reason for their higher sensitivity to such a treatment as compared with cells in the stationary phase of growth.

Repair of double-strand breaks in plasmid DNA in the yeast Saccharomyces cerevisiae.

We studied the repair of double-strand breaks (DSB) in plasmid DNA introduced into haploid cells of the yeast Saccharomyces cerevisiae. The efficiency of repair was estimated from the frequency of transformation of the cells by an autonomously replicated linearized plasmid. The frequency of "lithium" transformation of Rad+ cells was increased greatly (by 1 order of magnitude and more) compared with that for circular DNA if the plasmid was initially linearized at the XhoI site within the LYS2 gene. This effect is due to recombinational repair of the plasmid DNA. Mutations rad52, rad53, rad54 and rad57 suppress the repair of DSB in plasmid DNA. The kinetics of DSB repair in plasmid DNA are biphasic: the first phase is completed within 1 h and the second within 14-18 h of incubating cells on selective medium.

[Rapid postradiation recovery of yeasts: the relationship to gamma-induced reciprocal mitotic recombination and gene conversion]. / "Bystroe" postradiatsionnoe vosstanovlenie drozhzhei: sviaz' s gamma-indutsirovannoi retsiproknoi mitoticheskoi rekombinatsiei i gennoi konversiei.

gamma-induced reciprocal mitotic recombination and gene conversion have been studied under conditions inhibiting "rapid" postirradiation recovery of diploid yeast Saccharomyces cerevisiae. It turned out that, if the first postirradiation cell division occurs at higher KCl concentrations ("rapid" postirradiation recovery is inhibited), the frequency of mitotic reciprocal recombination within the gene ADE2-centromere region decreases. Keeping of irradiated cells (in the G1 phase of the cell division cycle) in water at 28 degrees C prior to plating on the selective agar containing 1.5 M KCl leads to smaller frequency of gene conversion lys2-25/lys2-22----Lys+, as compared with that for the cells immediately plated on the selective agar. Correlation has been found between the coefficient of gene conversion frequency decrease, due to postirradiation keeping in water, and "rapid" recovery efficiency. Interpretation of the data is based on the hypothesis that recombination repair of DNA double-strand breaks induced by ionizing radiation is responsible for "rapid" postirradiation recovery.

[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.

[The relationship of the processes of recovery from thermal and radiation damage in yeast cells]. / O sviazi protsessov vosstanovleniia ot termicheskikh i radiatsionnykh povrezhdenii u drozhzhevykh kletok.

Synergistic enhancement coefficient (SEC) achieves the maximum value within 2-3 hours of holding overheated (50 degrees C) and gamma-irradiated diploid cells of Sacch. cerevisiae in water at 28 degrees C; further holding leads to SEC dropping almost to the initial value. The maximum in the curve involved disappears if gamma-irradiated (overheated) cells were held in water at 28 degrees C for 2-3 hours before hyperthermic treatment (gamma-irradiation). There is no maximum in the curve discussed for haploid yeast cells, which are incapable of "rapid" post-irradiation recovering. The experimental data are interpreted from the point of view of reversible inhibition of yeast post-irradiation recovery by hyperthermia.

[Effect of rad 54 mutation on the ability of Saccharomyces cerevisiae cells to recover from radiation and thermal injury]. / Vliianie mutatsii rad 54 na sposobnost' drozhzhevykh kletok Saccharomyces cerevisiae vosstanovlivat'sia ot radiatsionnykh i termicheskikh povrezhdenii.

The diploid cells of Saccharomyces cerevisiae carrying rad 54 homozygous mutation do not exhibit an ability for any considerable "rapid" postirradiation and post-hyperthermic recovery. A pretreatment with high temperature (50 degrees C) increases the radiation response of mutant cells. Survival of cells overheated before gamma-irradiation is increased by keeping them in water for 2-6 h at 28 degrees C, while the corresponding value of survival for cells treated by each of the factors delivered separately remains constant in these conditions.

[Recovery of yeast cells following the combined action of hyperthermia and ionizing radiation]. / Vosstanovlenie drozhzhevykh kletok posle kombinirovannogo vozdeistviia gipertermii i ioniziruiushchei radiatsii.

Consecutive action of elevated temperature (50 degrees C) and gamma-irradiation on yeast cells Saccharomyces cerevisiae was studied. It was shown that yeast cells can recover from lethal thermal and radiation lesions after the combined action of the two factors. The efficiency of recovery does not depend upon the sequence of treatments. Heating (50 degrees C) before or after gamma-irradiation increases the radiation response of yeast when plating the cells on a nutrient agar containing 1.5 M KCl. The synergistic effect decreases with yeast cells kept in water at 28 degrees C before plating. The influence of one factor on the effectiveness of recovery from damages induced by the other was estimated.