Requirement of the Escherichia coli dnaA gene function for integrative suppression of dnaA mutations by plasmid R100-1

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Abstract
The phenotype of Escherichia coli dnaA missense and nonsense mutations was integratively suppressed by plasmid R100-1. The suppressed strains, however, could not survive when the dnaA function was totally inactivated. This was demonstrated by the inability of replacing the dnaA allele in the suppressed strain by a dnaA::Tn10 insertion using phage P1-mediated transduction. When the intact dnaA + allele was additionally supplied by a specialized transducing phage, λimm 21 dnaA +, which integrated at the att λ site on the E. coli chromosome, then the dnaA::Tn10 insertion, together with a δ oriC deletion, were able to be introduced into the suppressed strain. Thus, the mechanisms of dnaA function for oriC and for the replication origin of R100-1 may not be quite the same.