Mechanism of Mutation in Non-Dividing Cells

摘要

Stationary-phase mutation can be induced in non-dividing cells after exposure to environmental stress. The mutations require the SOS-induced, error- prone polymerase DAN pol IV and DNA double-strand break (DSB) repair and recombination proteins. Sex plasmid transfer proteins are required for mutation of lac on the F'.; transfer functions induce single-strand nicks that might become DSBs. We find that introducing specific breaks in cis to lac in the absence of transfer functions results in -1000-fold stimulation of Lac+ stationary-phase mutation, including both frameshift reversions and lac gene amplifications. The mutation requires recombination proteins and pol IV, implying that these components act downstream of DSBs. DSBs made in trans to lac promote Lac+ mutation only poorly. We suggest adaptive mutations result form error-prone DNA synthesis primed during recombination- mediated DSB-repair, and the small stimulation provided by DSBs in trans results form SOS induction and increased pol IV. Notabl, we report that DSBs made in trans can promote Lac+ mutation if a region of DNA homology with the trans plasmid is provided near lac. Finally, we find that DSBs are not sufficient to activate mutation: DSB- activated mutation has not been observed in rapidly growing cells and requires RpoS, the stationary-phase and general stress response regulator.