[Mechanism and kinetics of repair mutagenesis]

On the basis of experimental data a model of induced mutagenesis is proposed that takes into account the repair of DNA damage by the rec-system. The peculiar feature of the rec-system is the cleavage and resynthesis of long sequences near the recognized DNA-damage. Up to 100--2000 nucleotides are replaced in one act. Therefore a definite probability exists of finding a damaged point on the second strand serving as template. It is believed that at this point no requirements of complementary exist and that a random substitution can take place. This is the origin of point mutation. From the model a general formula for the dose-response curve of mutagenesis is deduced which also takes into account the possibility of simultaneously initiated repair on both complementary strands of DNA. The latter leads to a lethal event when the points are situated priximally. This formula fits the observations in different cases studied, for instance, in case of transition from uvr+ to uvr- strains. The absence of repair mutagenesis in case of transforming DNA damage is readily explained by one-strand integration.