A LOW-CA2-PESTIS( RESPONSE (LCR) SECRETION (YSC) LOCUS LIES WITHIN THE LCRB REGION OF THE LCR PLASMID IN YERSINIA)

The causative agent of plague, Yersinia pestis, contains a 75-kb plasm id, pCD1, which carries a virulence-related stimulon called the low-Ca 2+ response stimulon (LCRS). LCRS operons are regulated by the environ mental signals of temperature and Ca2+. This study characterized a por tion of the lcrB region of pCD1, known to contain at least one gene ne cessary for the regulation of LCRS operons by Ca2+. The sequence of a 2-kb region revealed three open reading frames, designated yscQ, yscR, and yscS, predicted to encode acidic proteins of 34.4, 24.4, and 8.5 kDa. All three proteins were homologous to proteins involved in flagel lar function or virulence. An antipeptide antibody specific for YscR w as used to localize YscR to the inner membrane of Y. pestis. Analysis of yscR-phoA fusions supported a model for yscR which predicts four tr ansmembrane regions and a large, central hydrophilic domain. In-frame deletion mutations of yscQ and yscR mere constructed and moved into Y. pestis. Both mutants failed to show the restriction of growth that no rmally accompanies maximal LCRS induction. Unlike the parent Y. pestis , the yscR mutant did not respond to the absence of Ca2+ by increasing the net transcription or translation of the LCRS-encoded V antigen, Y opM, or LcrG. The yscR mutant also was defective for secretion of V an tigen, YopM, and LcrG. These findings implicate a dual role for YscR i n regulation of LCRS operons and secretion of LCRS proteins and add to the developing picture of how secretion of virulence proteins may be coupled to transcriptional regulation in yersiniae.