Genetic analysis of DNA replication in bacteria: dnaB mutations that suppress dnaC mutations and dnaQ mutations that suppress dnaE mutations in Salmonella typhimurium.

We have isolated and characterized extragenic suppressors of mutations in two different target genes that affect DNA replication in Salmonella typhimurium. Both the target and the suppressor genes are functional homologues of known replication genes of E. coli that were identified in intergeneric complementation tests. Our results point to interactions in vivo involving the dnaB and dnaC proteins in one case and the dnaQ and dnaE proteins in the other case. The suppressor mutations, which were isolated as derivatives of lambda-Salmonella in vitro recombinants, were detected by an adaptation of the red plaque complementation assay. This method was applicable even when the locus of suppressor mutations was not chosen in advance.