A PLASMID-ENCODED PREPILIN PEPTIDASE GENE FROM ENTEROPATHOGENIC ESCHERICHIA-COLI

Enteropathogenic Escherichia coli, a leading agent of infantile diarrh ea world,vide, adheres to tissue culture cells in a pattern called ''l ocalized adherence.'' Localized adherence is associated with bundle-fo rming pill encoded by the plasmid bfpA gene, the product of which is h omologous with the major structural subunit proteins of type IV fimbri ae in other bacteria. Several of these proteins have been shown to be processed from a precursor by a specific prepilin peptidase. We cloned restriction fragments downstream of the bfpA gene into an E. coli-Pse udomonas aeruginosa shuttle vector and mobilized them into a P. aerugi nosa prepilin peptidase (pilD) mutant. A plasmid containing a 1.3-kb P stI-BamHI fragment was able to complement the pilD mutation, as demons trated by restoration of sensitivity to the pilus-specific bacteriopha ge PO4. The DNA sequence of this fragment revealed an open reading fra me, designated bfpP, the predicted product of which is homologous to o ther prepilin peptidases, including TcpJ of Vibrio cholerae (30% ident ical amino acids), PulO of Klebsiella oxytoca (29%), and PilD of P. ae ruginosa (28%). A bfpA::TnphoA mutant complemented with a bfpA-contain ing DNA fragment only partially processes the BfpA protein. When compl emented with a larger fragment containing bfpP as well as bfpA, the mu tant expresses the fully processed BfpA protein. P. aeruginosa PAK, bu t not a pilD mutant of PAK, expresses mature BfpA protein when the bfp A gene is mobilized into this strain. Thus, as in other type IV fimbri a systems, enteropathogenic E. coil utilizes a specific prepilin pepti dase to process the major subunit of the bundle-forming pilus. This pr epilin peptidase contains sequence and reciprocal functional homologie s with the PilD protein of P. aeruginosa.