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Journal of Bacteriology, February 1999, p. 731-739, Vol. 181, No. 3
Department of Molecular Microbiology and
Immunology, Oregon Health Sciences University, L220, Portland, Oregon
97201-3098,1 and
Howard Hughes Medical
Institute2 and
Department of
Biochemistry and Biophysics,3 School of
Medicine, University of California San Francisco, San Francisco,
California 94143-0448
Received 7 October 1998/Accepted 16 November 1998
The pilA gene of Neisseria gonorrhoeae was
initially identified in a screen for transcriptional regulators of
pilE, the expression locus for pilin, the major structural
component of gonococcal pili. The predicted protein sequence for PilA
has significant homology to two GTPases of the mammalian signal
recognition particle (SRP), SRP54 and SR
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Neisseria gonorrhoeae PilA Is an
FtsY Homolog
. Homologs of SRP54 and
SR were subsequently identified in bacteria (Ffh and FtsY,
respectively) and appear to form an SRP-like apparatus in prokaryotes.
Of the two proteins, PilA is the most similar to FtsY (47% identical
and 67% similar at the amino acid level). Like FtsY, PilA is essential
for viability and hydrolyzes GTP. The similarities between PilA and the
bacterial FtsY led us to ask whether PilA might function as the
gonococcal FtsY. In this work, we show that overproduction of PilA in
Escherichia coli leads to an accumulation of
pre-
-lactamase, similar to previous observations with other
bacterial SRP components. Low-level expression of pilA in
an ftsY conditional mutant can complement the
ftsY mutation and restore normal growth to this strain
under nonpermissive conditions. In addition, purified PilA can replace
FtsY in an in vitro translocation assay using purified E. coli SRP components. A PilA mutant that is severely affected in
its GTPase activity cannot replace FtsY in vivo or in vitro. However,
overexpression of the GTPase mutant leads to the accumulation of
pre--lactamase, suggesting that the mutant protein may interact with
the SRP apparatus to affect protein maturation. Taken together, these
results show that the gonococcal PilA is an FtsY homolog and that the
GTPase activity is necessary for its function.
*
Corresponding author. Mailing address: Department of
Molecular Microbiology and Immunology, Oregon Health Sciences
University, L220, 3181 SW Sam Jackson Park Rd., Portland, OR
97201-3098. Phone: (503) 494-6840. Fax: (503) 494-6862. E-mail:
arvidson{at}ohsu.edu.
Journal of Bacteriology, February 1999, p. 731-739, Vol. 181, No. 3
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
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