Stationary-phase mutation in the bacterial chromosome: Recombination protein and DNA polymerase IV dependence

Several microbial systems have been shown to yield advantageous mutations i n slowly growing or nongrowing cultures. In one assay system, the stationar y-phase mutation mechanism differs from growth-dependent mutation, demonstr ating that the two are different processes. This system assays reversion of a lac frameshift allele on an F ' plasmid in Escherichia coli. The station ary-phase mutation mechanism at lac requires recombination proteins of the RecBCD double-strand-break repair system and the inducible error-prone DNA polymerase IV, and the mutations are mostly -1 deletions in small mononucle otide repeats, This mutation mechanism is proposed to occur by DNA polymera se errors made during replication primed by recombinational double-strand-b reak repair. It has been suggested that this mechanism is confined to the F plasmid, However, the cells that acquire the adaptive mutations show hyper mutation of unrelated chromosomal genes, suggesting that chromosomal sites also might experience recombination protein-dependent stationary-phase muta tion. Here we test directly whether the stationary-phase mutations in the b acterial chromosome also occur via a recombination protein- and pol IV-depe ndent mechanism. We describe an assay for chromosomal mutation in cells car rying the F ' lac, We show that the chromosomal mutation is recombination p rotein- and pol IV-dependent and also is associated with general hypermutat ion, The data indicate that, at least in these male cells, recombination pr otein-dependent stationary-phase mutation is a mechanism of general inducib le genetic change capable of affecting genes in the bacterial chromosome.