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Journal of Bacteriology, April 2002, p. 2243-2250, Vol. 184, No. 8
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.8.2243-2250.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Roles of the C-Terminal End of SecY in Protein Translocation and Viability of Escherichia coli

Institute for Virus Research, Kyoto University, Kyoto 606-8507, Japan

Received 25 September 2001/ Accepted 20 January 2002

SecY, a central component of the membrane-embedded sector of protein translocase, contains six cytosolic domains. Here, we examined the importance of the C-terminal cytosolic region of SecY by systematically shortening the C-terminal end and examining the functional consequences of these mutations in vivo and in vitro. It was indicated that the C-terminal five residues are dispensable without any appreciable functional defects in SecY. Mutants missing the C-terminal six to seven residues were partially compromised, especially at low temperature or in the absence of SecG. In vitro analyses indicated that the initial phase of the translocation reaction, in which the signal sequence region of the preprotein is inserted into the membrane, was affected by the lack of the C-terminal residues. SecA binding was normal, but SecA insertion in response to ATP and a preprotein was impaired. It is suggested that the C-terminal SecY residues are required for SecA-dependent translocation initiation.

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