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J. Bacteriol., Aug 1995, 4779-4791, Vol 177, No. 16
J Haase, R Lurz, AM Grahn, DH Bamford and E Lanka
DNA transfer by bacterial conjugation requires a mating pair formation
(Mpf) system that specifies functions for establishing the physical contact
between the donor and the recipient cell and for DNA transport across
membranes. Plasmid RP4 (IncP alpha) contains two transfer regions
designated Tra1 and Tra2, both of which contribute to Mpf. Twelve
components are essential for Mpf, TraF of Tra1 and 11 Tra2 proteins, TrbB,
-C, -D, -E, -F, -G, -H, -I, -J, -K, and -L. The phenotype of defined
mutants in each of the Tra2 genes was determined. Each of the genes, except
trbK, was found to be essential for RP4- specific plasmid transfer and for
mobilization of the IncQ plasmid RSF1010. The latter process did not
absolutely require trbF, but a severe reduction of the mobilization
frequency occurred in its absence. Transfer proficiency of the mutants was
restored by complementation with defined Tra2 segments containing single
trb genes. Donor-specific phage propagation showed that 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-encoded receptor complex. Strains
containing the Tra2 plasmid in concert with traF were found to overexpress
trb products as well as extracellular filaments visualized by electron
microscopy. Each trb gene and traF are needed for the formation of the
pilus-like structures. The trbK gene, 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 context of related macromolecule export
systems.
Copyright © 1995, American Society for Microbiology
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
Max-Planck-Institut fur Molekulare Genetik, Dahlem, Berlin, Germany.
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