A program of Yersinia enterocolitica type III secretion reactions is activated by specific signals

Successful establishment of Yersinia infections requires the type III machi nery, a protein transporter that injects virulence factors (Pops) into macr ophages. It is reported here that the Yersinia type III pathway responds to environmental signals by transporting proteins to distinct locations. Yers inia enterocolitica cells sense an increase in extracellular amino acids (g lutamate, glutamine, aspartate, and asparagine) that results in the activat ion of the type III pathway. Another signal, provided by serum proteins suc h as albumin, triggers the secretion of YopD into the extracellular medium. The third signal, a decrease in calcium concentration, appears to be provi ded by host cells and causes Y. enterocolitica to transport YopE and presum ably other virulence factors across the eukaryotic plasma membrane. Mutatio ns in several genes encoding regulatory molecules (lcrG, lcrH, tyeA, yopD, yopN yscM1, and yscM2) bypass the signal requirement of the type III pathwa y. Together these results suggest that yersiniae may have evolved distinct secretion reactions in response to environmental signals.