THE SALMONELLA-TYPHIMURIUM INVASION GENES INVF AND INVG ENCODE HOMOLOGS OF THE ARAC AND PULD FAMILY OF PROTEINS

We have identified two novel Salmonella typhimurium. genes, invF and i nvG, which are required for the efficient entry of these organisms int o cultured epithelial cells. invF and invG are located immediately ups tream of invE, a previously identified gene also required for Salmonel la entry. Non-polar mutations in these genes rendered S. typhimurium s everely deficient for entry into cultured epithelial cells. The nucleo tide sequences of invF and invG indicated that these genes encode poly peptides with predicted molecular weights of 24 373 and 62 275, respec tively. Proteins of similar sizes were observed when invF and invG wer e expressed in a bacteriophage T7 RNA polymerase-based expression syst em. Comparison of the predicted sequence of InvF with translated seque nces in the existing databases indicated that this protein is homologo us to members of the AraC family of prokaryotic transcription regulato rs. However, mutations in invF did not significantly affect the expres sion of other members of the inv locus, InvG was found to be homologou s to members of the Pulp family of specialized translocases. This homo logy suggests that InvG may be necessary for the export of invasion-re lated determinants or involved in the assembly of a supramolecular str ucture that promotes entry.