dnaB gene of Escherichia coli K-12 affects superinfection inhibition between F' plasmids.

F' Escherichia coli K-12 strains bearing the chromosomal mutation dnaB43 offer significantly less resistance to the conjugational introduction of a second F' plasmid than do nonmutant strains. Both the entry exclusion and incompatibility components of superinfection inhibition are altered. This action of dnaB43 occurs regardless of the presence of a recA-minus mutation in matings in liquid cultures and on membrane filters and is not limited to a particular set of F' plasmids. These effects are co-transducible by phage P1 with the temperature sensitivity conferred by dnaB43. The effects also occur with a strain carrying dnaB107. In the double F' strains that arise, the two plasmids exist as units autonomous of one another and the chromosome.