COMPARISON OF THE PROMOTER PROXIMAL REGIONS OF THE TOXIN-CO-REGULATEDTCP GENE-CLUSTER IN CLASSICAL AND EL-TOR STRAINS OF VIBRIO-CHOLERAE O1

A physical map has been constructed of the 5-kb XbaI fragment encoding the promoter proximal of region the tcp gene cluster encoding the tox in-coregulated pilus (TCP) of Vibrio cholerae. This fragment contains the major regulatory regions for TCP. Comparison of the nucleotide (nt ) sequences from strains of the classical and El Tor biotypes demonstr ates that the regions are essentially identical, with several notable exceptions, The intergenic regions, between tcpI and tcpP, and between tcpH and tcpA, show significant sequence divergence which may account for the biotype-related differences in TCP, since this is the locatio n of the major promoter sequences. The C-terminal coding regions of th e major pilin subunit, TcpA, also differ. Southern hybridization analy ses suggest that the tcpA nt sequence is conserved within a biotype, a nd Western blot analysis suggests that the two forms of TcpA are antig enically different, but related. Besides tcpA, tcpB, tcpH and tcpI, th e genes encoding two additional proteins, TcpP and TcpQ, but not previ ously defined, were also identified, TcpH and TcpI have been previousl y suggested to be regulatory proteins but homology data imply that Tcp I is a methyl-accepting chemotaxis protein (MCP), as recently reported [Harkey et al., Infect, Immun, 62 (1994) 2669-2678], and TcpH is pred icted to be a periplasmic or exported protein. TcpP is thought to be a trans-cytoplasmic membrane (CM) protein which may have a regulatory r ole.