A Salmonella typhimurium virulence protein is similar to a Yersinia enterocolitica invasion protein and a bacteriophage lambda outer membrane protein.

The phoP-phoQ-regulated pagC locus is essential for full virulence and survival within macrophages of Salmonella typhimurium. The protein product, DNA sequence, and transcript of pagC were determined. The pagC locus encodes a single 188-amino-acid membrane protein that is similar to the ail-encoded eucaryotic cell invasion protein of Yersinia enterocolitica and the lom-encoded protein of bacteriophage lambda. The similarity of PagC and Ail to Lom leads us to hypothesize that Lom is a virulence protein and that bacteriophage gene transfer and lysogeny could have led to the development of proteins essential to survival within macrophages and eucaryotic cell invasion.