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J. Bacteriol., Sep 1997, 5728-5735, Vol 179, No. 18
J Haase and E Lanka
TraF, an essential component of the conjugative transfer apparatus of the
broad-host-range plasmid RP4 (IncP), which is located at the periplasmic
side of the cytoplasmic membrane, encodes a specific protease. The traF
gene products of IncP and Ti plasmids show extensive similarities to
prokaryotic and eukaryotic signal peptidases. Mutational analysis of RP4
TraF revealed that the mechanism of the proteolytic cleavage reaction
resembles that of signal and LexA-like peptidases. Among the RP4 transfer
functions, the product of the Tra2 gene, trbC, was identified as a target
for the TraF protease activity. TrbC is homologous to VirB2 of Ti plasmids
and thought to encode the RP4 prepilin. The maturation of TrbC involves
three processing reactions: (i) the removal of the N-terminal signal
peptide by Escherichia coli signal peptidase I (Lep), (ii) a proteolytic
cleavage at the C terminus by an as yet unidentified host cell enzyme, and
(iii) C-terminal processing by TraF. The third reaction of the maturation
process is critical for conjugative transfer, pilus synthesis, and the
propagation of the donor-specific bacteriophage PRD1. Thus, cleavage of
TrbC by TraF appears to be one of the initial steps in a cascade of
processes involved in export of the RP4 pilus subunit and pilus assembly
mediated by the RP4 mating pair formation function.
Copyright © 1997, American Society for Microbiology
A specific protease encoded by the conjugative DNA transfer systems of IncP and Ti plasmids is essential for pilus synthesis
Max-Planck-Institut fur Molekulare Genetik, Berlin, Germany.
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