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J. Bacteriol., Dec 1996, 6720-6729, Vol 178, No. 23
J Haase, M Kalkum and E Lanka
TrbK is the only plasmid-encoded gene product involved in entry exclusion
of the broad-host-range plasmid RP4. The corresponding gene, trbK, coding
for a protein of 69 amino acid residues maps in the Tra2 region within the
mating pair formation genes. TrbK carries a lipid moiety at the N-terminal
cysteine of the mature 47-residue polypeptide. The mutant protein TrbKC23G
cannot be modified or proteolytically processed but still acts in entry
exclusion with reduced efficiency. An 8-amino-acid truncation at the C
terminus of TrbK results in a complete loss of the entry exclusion activity
but still allows the protein to be processed. TrbK localizes predominately
to the cytoplasmic membrane. Its function depends on presence in the
recipient cell but not in the donor cell. TrbK excludes plasmids of
homologous systems of the P complex; it is inert towards the IncI system.
The likely target for TrbK action is the mating pair formation system,
because DNA or any of the components of the relaxosome were excluded as
possible targets.
Copyright © 1996, American Society for Microbiology
TrbK, a small cytoplasmic membrane lipoprotein, functions in entry exclusion of the IncP alpha plasmid RP4
Max-Planck-Institut fur Molekulare Genetik, Dahlem, Berlin, Germany.
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