[Molecular mechanisms of stress-induced hereditary variability].

The molecular mechanisms of generation of stress-induced genetic recombinations and point mutations are considered. Due to the oxidative, temperature, radiation and other forms of stress, intensive modification of DNA bases occurs. Excision of the modified bases (hypoxanthine, uracil, pyrimidine photoproducts, methylated purines) leads to the formation of single-stranded gaps in DNA. If one DNA strand is damaged, there is high probability of its primary structure being completely restored. When the rate of lesions increases, the DNA can be damaged in the gap-related opposite sites of both strands. It is shown that in this case, the excision repair leads to a burst of recombinations and point mutations which may be concerned with the mispairings, double-stranded breaks, induction of SOS-response. With the increase in the rate of lesions, the possibility of the damage in self-complementary DNA sequences is also enhanced. This leads to formation of hairpin structures in the single-stranded DNA stretches. It is demonstrated that in these cases the repair results in development of deletions, insertions and clusters of point mutations predetermined by the primary DNA structure. Independent means of stress-induced mutations' occurrence seem to be the transposable elements. The stress-induced outbreaks of recombinations provide conceivably new variants of genotypes to be selected for the adaptation to new extreme conditions.