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Journal of Bacteriology, September 2005, p. 6454-6465, Vol. 187, No. 18
0021-9193/05/$08.00+0     doi:10.1128/JB.187.18.6454-6465.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Modeling the Effects of prl Mutations on the Escherichia coli SecY Complex

Margaret A. Smith,¹ William M. Clemons Jr.,² Cathrine J. DeMars,^1, and Ann M. Flower^1*

Department of Microbiology and Immunology, University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota 58202-9037,¹ Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115²

Received 4 April 2005/ Accepted 22 June 2005

The apparatus responsible for translocation of proteins across bacterial membranes is the conserved SecY complex, consisting of SecY, SecE, and SecG. Prior genetic analysis provided insight into the mechanisms of protein export, as well as the interactions between the component proteins. In particular, the prl suppressor alleles of secE and secY, which allow export of secretory proteins with defective signal sequences, have proven particularly useful. Here, we report the isolation of novel mutations in secE and secY, as well as the phenotypic effects of combinations of prl mutations. These new alleles, as well as previously characterized prl mutations, were analyzed in light of the recently published crystal structure of the archaeal SecY complex. Our results support and expand a model of Prl suppressor activity that proposes that all of the prlA and prlG alleles either destabilize the closed state of the channel or stabilize the open form. These mutants thus allow channel opening to occur without the triggering event of signal sequence binding that is required in a wild-type complex.

Present address: Gastroenterology Research Unit, Mayo Clinic, Rochester, MN.

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