Gene cluster for assembly of pilus colonization factor antigen III of enterotoxigenic Escherichia coli

The assembly of pilus colonization factor antigen III (CFA/III) of enteroto xigenic Escherichia coli (ETEC) requires the processing of CFA/III major pi lin (CofA) by a prepilin peptidase (CofP), similar to other type IV pilus f ormation systems. CofA is produced initially as a 26.5-kDa preform pilin (p repilin) and then processed to a 20.5-kDa mature pilin by CofP which is pre dicted to be localized in the inner membrane. In the present experiment, we determined the nucleotide sequence of the whole region for CFA/III formati on and identified a cluster of 14 genes, including cofA and cofP. Several p roteins encoded by cof genes were similar to previously described proteins, such as the toxin-coregulated pili of Vibrio cholerae and the bundle-formi ng pill of enteropathogenic E. coli. The G+C content of the cof gene cluste r was 37%, which was significantly lower than the average for the E. coli g enome (50%). The introduction of a recombinant plasmid containing the cof g ene cluster into the E. coli K-12 strain conferred CFA/III biogenesis and t he ability of adhesion to the human colon carcinoma cell line Caco-2. This is the first report of a complete nucleotide sequence of the type IV pili f ound in human ETEC, and our results provide a useful model for studying the molecular mechanism of CFA/III biogenesis and the role of CFA/III in ETEC infection.