THE CHAPERONE-LIKE PROTEIN YERA OF YERSINIA-PSEUDOTUBERCULOSIS STABILIZES YOPE IN THE CYTOPLASM BUT IS DISPENSIBLE FOR TARGETING TO THE SECRETION LOCI

The virulence plasmid-encoded YopE cytotoxin of Yersinia pseudotobercu losis is secreted across the bacterial membranes and subsequently tran slocated into the eukaryotic cell. Translocation of YopE into target c ells was recently shown to be polarized and only occurred at the zone of contact between the pathogen and the eukaryotic cell. Immunogold el ectron microscopy on cryosectioned Y. pseudotuberculosis revealed that YopE is secreted and deposited on the bacterial cell surface when the bacteria are grown in Ca2+-depleted media at 37 degrees C. No YopE wa s detected in the cytoplasm or in the membranes. In yerA mutants which are downregulated for YopE at a post-transcriptional level, the cytot oxin could only be detected in the cytoplasm. The overall recovery of YopE from the yerA mutant strain was, however, considerably lower than from the wild-type strain. yerA had no major effect on the translatio n of YopE, but was found to stabilize YopE in the cytoplasm. YerA was shown to specifically interact with YopE in the cytoplasm in vivo and this binding also correlated with YopE secretion. Targeting of YopE to the secretion loci as well as translocation of YopE into HeLa cells o ccurred also in the absence of YerA. Based on our findings, we suggest that YerA by binding to YopE stabilizes and maintains the cytotoxin i n a secretion-competent conformation.