Induction of the SOS system produced by radiations with different linear energy transfer

Induction of the bacterial SOS by radiation with different LET using the method of SOS-chromo-test and λ-prophage induction is investigated. The effectiveness of the SOS response induced augments parallel to the increasing LET, reaching a maximum about 40-60 keV/μm, and thereby decreasing at greater LET values. The assumption is warranted that damages starting the SOS system are of a complex type, i.e. severe single stranded disruptions of DNA generated by substantial amounts of energy deposition within DNA molecule. At greater LET values damaging radiation effectiveness decreases owing to energy fluctuation in the heavy ionizing particles. Comparison of the λ-induction curves of cells with different genotype points to the major of slow RecA-lexA-dependent repair, as compared to the fast polA-dependent one. The difference between radiosensitivity of lysogenic and non-lysogenic cells is explained as resulting from competition between the two repressors - LexA and λ- in the process of their cleavage by the RecA protein