THE SALMONELLA-TYPHIMURIUM INVH PROTEIN IS AN OUTER-MEMBRANE LIPOPROTEIN REQUIRED FOR THE PROPER LOCALIZATION OF INVG

The secretion of pathogenicity factors by Salmonella typhimurium is me diated by a type III secretion system that includes an outer membrane protein of the secretin family. Related secretins are also required fo r f1 phage assembly and type II secretion. When the C-terminal 43 amin o acids of the S. typhimurium secretin InvG are added to f1 pIV, the c himeric f1 pIV-'lnvG(43) protein becomes dependent on the co-expressio n of another gene, invH, for function in phage assembly. [H-3]-palmiti c acid labelling, globomycin sensitivity and density gradient flotatio n were used to demonstrate that InvH is an outer membrane lipoprotein that is processed by signal peptidase II. A complex between chimeric f 1 plV-'InvG(43) and InvH was demonstrated in vivo. InvH was shown to b e required for the proper localization of InvG in the outer membrane a nd for the secretion of the virulence factor SipC. These results sugge st that InvH and InvG are part of the functional outer membrane transl ocation complex in type III secretion systems.