Although nonconjugative mobilizable plasmids require helping functions of conjugative plasmids in order to be mobilized into recipients, at least some genes from the nonconjugative plasmids may be induced to assist in the DNA transfer process. Conjugative plasmids from 12 different incompatibility groups mobilized the nonconjugative plasmid ColE1Ap between Escherichia coli strains. Introduction of any of the conjugative plasmids into the ColE1Ap-containing strain resulted in an induction of mbeC, the product of which is a component of the mobilization relaxation complex. Each of the conjugative plasmids caused protein to bind specifically to mbe promoter DNA, suggesting a direct regulatory interaction.