Surface exclusion between F' plasmids in strains of Escherichia coli K-12 carrying a dnaB mutation, in the presence or absence of bacteriophage genomes providing a dnaB analog function.

In a set of isogenic strains, three out of four different dnaB(ts) mutations reduced surface exclusion between F' plasmids. In further studies with a strain carrying one of these mutations (dnaB43), surface exclusion remained reduced in the presence of a recombinant plasmid carrying only the region of F that encodes the surface exclusion proteins TraSp and TraTp. The dnaB analog specified by bacteriophage P1 but not that specified by P7 increased the surface excluding ability of the strain carrying dnaB43 to the same level as the isogenic dnaB+ strain. The possible role of the dnaB gene in surface exclusion is discussed.