Journal of Bacteriology, December 2001, p. 6979-6990, Vol. 183, No. 24
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.24.6979-6990.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Howard Hughes Medical Institute, Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York 10461,1 and Department of Microbiology and Immunology, University of North Carolina, Chapel Hill, North Carolina 27599-72902
Received 22 June 2001/Accepted 18 September 2001
The proper extracytoplasmic localization of proteins is an
important aspect of mycobacterial physiology and the pathogenesis of
Mycobacterium tuberculosis. The protein export systems
of mycobacteria have remained unexplored. The Sec-dependent protein
export pathway has been well characterized in Escherichia
coli and is responsible for transport across the cytoplasmic
membrane of proteins containing signal sequences at their amino
termini. SecA is a central component of this pathway, and it is highly
conserved throughout bacteria. Here we report on an unusual property of
mycobacterial protein export
the presence of two homologues of SecA
(SecA1 and SecA2). Using an allelic-exchange strategy in
Mycobacterium smegmatis, we demonstrate that
secA1 is an essential gene. In contrast,
secA2 can be deleted and is the first example of a
nonessential secA homologue. The essential nature of
secA1, which is consistent with the conserved Sec
pathway, leads us to believe that secA1 represents the
equivalent of E. coli secA. The results of a phenotypic analysis of a
secA2 mutant of M.
smegmatis are presented here and also indicate a role for SecA2
in protein export. Based on our study, it appears that SecA2 can assist
SecA1 in the export of some proteins via the Sec pathway. However,
SecA2 is not the functional equivalent of SecA1. This finding, in
combination with the fact that SecA2 is highly conserved throughout
mycobacteria, suggests a second role for SecA2. The possibility exists
that another role for SecA2 is to export a specific subset of proteins.
Present address: Aaron Diamond AIDS Research Center, New York, NY 10016.
This article has been cited by other articles:
| Appl. Environ. Microbiol. | Infect. Immun. | Eukaryot. Cell |
|---|---|---|
| Mol. Cell. Biol. | J. Virol. | Microbiol. Mol. Biol. Rev. |
| ALL ASM JOURNALS |