The product of the F sex factor traT surface exclusion gene is a lipoprotein

The product of the Escherichia coli sex factor F traT gene (TraTp), an outer membrane protein of Mr = 25,000, is covalently modified in vivo by the addition of glycerol and fatty acids. Consistent with this result, and as would be expected for a bacterial lipoprotein, the novel amino acid glycerylcysteine can be detected in purified TraTp. Being a secreted protein, TraTp is made from a signal sequence containing precursor, and glycerol and fatty acids can be detected in both the precursor and mature (processed) species of TraTp. The peptide antibiotic globomycin inhibits the cleavage of the pro-TraTp signal sequence, but not the glycerol and fatty acid modification. Diglyceride modification of the Cys residue at the site of signal sequence cleavage probably precedes and is a prerequisite for processing of the TraTp signal sequence. Thus, TraTp appears to be a typical E. coli lipoprotein, having a pathway for modification and processing that is similar to that of Braun's lipoprotein (the major outer membrane lipoprotein).