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Journal of Bacteriology, September 2008, p. 6204-6216, Vol. 190, No. 18
0021-9193/08/$08.00+0 doi:10.1128/JB.00467-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Department of Microbiology, University of Chicago, Chicago, Illinois 60637
Received 5 April 2008/ Accepted 20 June 2008
Yersinia type III machines secrete protein substrates across the bacterial envelope and, following assembly of their secretion needles, transport effector Yops into host cells. According to their destination during type III secretion, early, middle, and late secretion substrates can be distinguished; however, the signals and mechanisms whereby these proteins are recognized and transported by the secretion machine are not understood. Here, we examine several hybrids between secretion substrates and the impassable reporter protein glutathione S-transferase (GST). YscP-GST and YopR-GST blocked type III secretion; however, YscF-, YopD-, YopN-, and LcrV-GST did not. Unlike YopR-GST, which can block type III machines only during their assembly, expression of YscP-GST led to an immediate and complete block of all secretion. The secretion signal of YscP was mapped to its first 10 codons or amino acids; however, YscP
2-15-GST, lacking this secretion signal, imposed a partial blockade. YscP-GST copurified with the type III ATPase complex (YscN, YscL, and YscQ) and with YscO, suggesting that the association of specific machine components with the impassable substrate may cause the block in type III secretion.
Published ahead of print on 18 July 2008.
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