Effect of the adaptive response on the induction of the SOS pathway in E. coli K-12.

The adaptive-response is an inducible repair system of E. coli which reduces the mutagenic and cytotoxic effects of alkylation damage (Samson and Cairns, 1977). In adapted cells (cells exposed to sublethal doses of alkylating agents) the induction of W-reactivation and W-mutagenesis by alkylating agents is almost totally blocked. Despite the fact that adaptation has no detectable effect on UV mutagenesis in E. coli K-12, it does inhibit to some extent the UV and tif-1 mediated induction of SOS functions such as W-reactivation and lambda prophage induction. Furthermore, the kinetics of induction of W-mutagenesis following UV treatment are altered by adaptation. In this case the adaptive-response seems to specifically block the induction of an error-producing W-reactivating capacity which normally would increase soon after UV treatment, while affecting error-free W-reactivating systems to a lesser extent.