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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.

Neisseria gonorrhoeae PilA Is an FtsY Homolog

Cindy Grove Arvidson,1,* Ted Powers,2,3 Peter Walter,2,3 and Magdalene So1

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 SRalpha . Homologs of SRP54 and SRalpha 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-beta -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-beta -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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