The Yersinia enterocolitica GsrA stress protein, involved in intracellular survival, is induced by macrophage phagocytosis.

The Yersinia enterocolitica gsrA gene is a stress protein gene which was originally identified as essential for protecting cells under both extracellular environmental stress and intracellular stress in macrophages due to phagocytosis. The gsrA gene was shown to be a member of the htrA class of genes and to possess a sequence homologous to that of the promoter recognized by a stress-induced sigma factor, sigmaE. In order to study the induction of the potentially sigmaE-controlled gsrA gene in Y. enterocolitica after phagocytosis by macrophages, we identified GsrA by overproducing the protein using a T7 promoter-gsrA fusion. We found that it is translated as an unstable 49,500-Da protein which is processed by removal of an amino acid fragment consisting of 27 residues, resulting in a stable 46,800-Da protein. By radiolabeling proteins specific to bacteria in the J774-1 macrophage-like cell line, we found that the production of GsrA protein is indeed enhanced in bacterial cells growing within macrophage phagosomes. Transcriptional activation of the gsrA gene was determined by using the gsrA promoter-lacZ fusion system. This work provides the first piece of evidence that the sigmaE regulon responds to the stressful environment found in macrophages.