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J Bacteriol. 2007 Sep;189(17):6469-73. Epub 2007 Jun 15.

Determinants of entry exclusion within Eex and TraG are cytoplasmic.

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Department of Molecular Biology and Microbiology, Tufts University School of Medicine, and Channing Laboratory, Brigham and Women's Hospital, Harvard Medical School, 181 Longwood Ave., Boston, MA 02115, USA.


We report here functional and topological analyses of TraG and Eex, the donor and recipient cell inner membrane proteins that mediate entry exclusion in the SXT/R391 family of integrative conjugative elements. We found that the exclusion-determining regions of the Eex variants EexS (SXT) and EexR (R391) are located in distinct yet overlapping regions of the proteins. Unexpectedly, the carboxyl-terminal regions of TraG and Eex, which contain the residues essential for exclusion activity and specificity, were found to localize in the cell cytoplasm. These observations suggest that complex topological rearrangements of conjugative proteins must occur during mating to enable these domains to interact.

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