VirG, a Yersinia enterocolitica lipoprotein involved in Ca2+ dependency, is related to exsB of Pseudomonas aeruginosa

Pathogenic yersiniae require Ca2+ for growth at 37 degrees C. They harbor closely related plasmids of about 70 kb that are essential for virulence. At 37 degrees C and in the absence of Ca2+ ions, these plasmids cause a decrease in growth rate and the release of large amounts of proteins called Yops. Here we describe the virG gene of Yersinia enterocolitica; virG is located just upstream of the virF gene, which encodes the transcriptional activator of some plasmid virulence factors. Analysis of the VirG amino acid sequence suggested that virG encodes a lipoprotein, which was confirmed by [3H]palmitate labeling of VirG-PhoA fusion proteins. A nonpolar virG mutant was constructed and found to be Ca2+ independent for growth at 37 degrees C but to still secrete Yops. This phenotype was complemented by the introduction of a plasmid harboring an intact virG gene. VirG was found to be homologous to ExsB, a protein encoded by a Pseudomonas aeruginosa gene located in the locus controlling exoenzyme S synthesis. Interestingly, the exsA gene, located just downstream of exsB, is also homologous to virF.