Regulation by Ca²⁺ in the Yersinia low‐Ca²⁺ response

The Yersinia low‐Ca²⁺ response (LCR) is a regulatory response in which a set of plasmid‐borne operons is transcriptionally regulated at 37°C in response to the presence or absence of mM concentrations of Ca²⁺. LCR‐regulated operons encode secreted proteins with regulatory and virulence roles as well as non‐secreted regulatory proteins and components of the secretion machinery. Downregulation by Ca²⁺ is imposed by a signalling 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 inner‐membrane protein with homologues in several virulence‐associated and flagella assembly‐related systems in diverse bacterial species. The mechanism of signal transduction in response to Ca²⁺ is not known, and the proteins that bind DNA to downregulate transcription have not been identified.