BACTERIAL CONJUGATION MEDIATED BY PLASMID RP4 - RSF1010 MOBILIZATION,DONOR-SPECIFIC PHAGE PROPAGATION, AND PILUS PRODUCTION REQUIRE THE SAME TRA2 CORE COMPONENTS OF A PROPOSED DNA TRANSPORT COMPLEX

DNA transfer by bacterial conjugation requires a mating pair formation (Mpf) system that specifies functions for establishing the physical c ontact between the donor and the recipient cell and for DNA transport across membrane. Plasmid RP4 (IncP alpha) contains two transfer region s designated Tra1 and Tra2, both of which contribute of Mpf. Twelve co mponents are essential for Mpf, TraF of Tra1 and 11 Tra2 proteins, Trb B, -C, -D, -E, -F, -G, -H, -I, -J, -K, and -L. The phenotype of define d mutants in each of the Tra2 genes was determined. Each of the genes, except trbK, was found to be essential for RP4-specific plasmid trans fer and for mobilization of the IncQ plasmid RSF1010. The latter proce ss did not absolutely require trbF, but a severe reduction of the mobi lization frequency occurred in its absence. Transfer proficiency of th e mutants was restored by complementation with defined Tra2 segments c ontaining single trb genes. Donor-specific phage propagation showed th at traF and each of the genes encoded by Tra2 are involved. Phage PRD1 , however, still adsorbed to the trbK mutant strain but not to any of the other mutant strains, suggesting the existence of a plasmid-encode d receptor complex. Strains containing the Tra2 plasmid in concert wit h traF were found to overexpress trb products as well as extracellular filaments visualized by electron microscopy. Each trb gene and traF a re needed for the formation of the pilus-like structures. The trbK gen e, which is required for PRD1 propagation and for pilus production but not for DNA transfer on solid media, encodes the RP4 entry-exclusion function. The components of the RP4 Mpf system are discussed in the co ntext of related macromolecule export systems.