MicroReview Reguiation by 2 + in the Yersinia low - Ca "̂ response

The Yersinia low-Ca^* response (LCR) is a reguiatory response in which a set of plasmid-borne operons is transcriptionaiiy regulated at 37 C in response to the presence or absence of mM concentrations of Ca^ .̂ LCR-reguiated operons encode secreted proteins with reguiatory and viruience roies as well as nonsecreted reguiatory proteins and components of the secretion machinery. Downregulation by Ca^* is imposed by a signaiimg cascade that includes secreted proteins and possibly also components of the secretion system and is hypothesized to act on membrane-bound inductive components. An important rote in LCR induction is played by LcrD, an innermembrane protein with homoiogues in several virulence-associated and flageiia assembly-reiated systems in diverse bacteriai species. The mechanism of signal transduction in response to Ca^* is not known, and the proteins that bind DNA to downregulate transcription have not been identified.