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Journal of Bacteriology, February 2008, p. 1413-1418, Vol. 190, No. 4
0021-9193/08/$08.00+0     doi:10.1128/JB.01633-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Additional In Vitro and In Vivo Evidence for SecA Functioning as Dimers in the Membrane: Dissociation into Monomers Is Not Essential for Protein Translocation in Escherichia coli{triangledown}

Hongyun Wang, Bing Na, Hsiuchin Yang, and Phang C. Tai*

Department of Biology, Georgia State University, Atlanta, Georgia 30303

Received 8 October 2007/ Accepted 28 November 2007

SecA is an essential component in the Sec-dependent protein translocation pathway and, together with ATP, provides the driving force for the transport of secretory proteins across the cytoplasmic membrane of Escherichia coli. Previous studies established that SecA undergoes monomer-dimer equilibrium in solution. However, the oligomeric state of functional SecA during the protein translocation process is controversial. In this study, we provide additional evidence that SecA functions as a dimer in the membrane by (i) demonstration of the capability of the presumably monomeric SecA derivative to be cross-linked as dimers in vitro and in vivo, (ii) complementation of the growth of a secA(Ts) mutant with another nonfunctional SecA or (iii) in vivo complementation and in vitro function of a genetically tandem SecA dimer that does not dissociate into monomers, and (iv) formation of similar ring-like structures by the tandem SecA dimer and SecA in the presence of lipid bilayers. We conclude that SecA functions as a dimer in the membrane and dissociation into monomers is not necessary during protein translocation.

* Corresponding author. Mailing address: Department of Biology, Georgia State University, 402 Kell Hall, 24 Peachtree Center Avenue, Atlanta, GA 30303. Phone: (404) 413-5303. Fax: (404) 413-5301. E-mail: biopct{at}langate.gsu.edu

{triangledown} Published ahead of print on 7 December 2007.

Journal of Bacteriology, February 2008, p. 1413-1418, Vol. 190, No. 4
0021-9193/08/$08.00+0     doi:10.1128/JB.01633-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

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  • Das, S., Stivison, E., Folta-Stogniew, E., Oliver, D. (2008). Reexamination of the Role of the Amino Terminus of SecA in Promoting Its Dimerization and Functional State. J. Bacteriol. 190: 7302-7307 [Abstract] [Full Text]  


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