[Quasi-adaptive response to alkylating agents in Escherichia coli: a new phenomenon].

An original hypothesis of a quasi-adaptive response to nitrosomethylurea (NMU) in Escherichia coli cells was verified experimentally. In contrast to the true Ada response, which is induced in cells pretreated with a sublethal dose of NMU, a quasi-adaptive response was induced using NO-containing dinitrosyl iron complex with glutathione (DNICglu). Quasi-adaptation increased expression of the Ada regulon and cell resistance to the cytotoxic and mutagenic effects of NMU. The levels of alkA, alkB, and aidB gene expression in quasi-adaptation were higher than in the true Ada response. Thus, experimental evidence was obtained for the alternative mechanism regulating the function of the Ada sensory protein in controlling expression of the Ada regulon during the adaptive response. The free iron--chelating agent o-phenanthroline (OP) facilitated degradation of DNICglu (by electron paramagnetic resonance (EPR) spectra) and considerably or completely inhibited gene expression in the quasi-adaptive response. The new phenomenon extends the functional range of NO compounds to include a role in genetic signal transduction within the Ada response system in addition to similar roles in the SoxRS, SOS, and OxyR systems in E. coli.