[The repair of UV-induced postreplication DNA gaps in Escherichia coli cells adapted to methylmethane sulfonate and ethylmethane sulfonate].

The survival (only after the adaptation to methylmethane sulfonate, MMS) and repair of DNA postreplication gaps in UV-irradiated Escherichia coli, adapted to MMS (20 mkg/ml for 3 h) and ethylmethane sulfonate (EMS, 100 mkg/ml for 3 h), have been investigated. The survival of MMS-adapted bacteria of wild strains B/r and K12 AB1157 somewhat increased, whereas the survival of AB1886 uvrA mutant, which unlike the wild type bacteria is unable to excise cyclobutane pyrimidine dimers, was seen to decrease. The repair of postreplicative gaps in MMS-adapted bacteria correlates qualitatively with changes in survival: in B/r and AB1157 strains the repair is somewhat more effective (10-15%), while in AB1886 uvrA mutant significantly slower (near 30%) than in non-adapted bacteria. Similar changes of postreplicative repair (PRR) of DNA are observed in AB1157 and AB1886 uvrA strains adapted to EMS. It is suggested that the decreased efficiency of PRR in bacteria AB1886 uvrA, adapted to alkylating agent, may be due to the interference between the two inducible repair processes: adaptive response and SOS response. The latter process is involved in the repair of some part of postreplicative gaps of DNA. Different results of PRR of DNA in bacteria of wild types, adapted to MMS and EMS, may be associated with the intrinsic PRR in uvr+ strains. Due to this process in uvr+ bacteria SOS component of PRR of DNA is not formed. It is suggested that PRR in uvr+ bacteria adapted to alkylating agents is accelerated by enzymes of adaptive response in the absence of antagonism between the SOS response and the adaptive response.