Genetic and transcriptional analyses of the Vibrio cholerae mannose-sensitive hemagglutinin type 4 pilus gene locus

The mannose-sensitive hemagglutinin (MSHA) of the Vibrio cholerae O1 EI Tor biotype is a member of the family of type 4 pill, Type 4 pill are found on the surface of a variety of gram-negative bacteria and have demonstrated i mportance as host colonization factors, bacteriophage receptors, and mediat ors of DNA transfer. The gene locus required for the assembly and secretion of the MSHA pilus has been localized to a 16.7-kb region of the V. cholera e chromosome. Sixteen genes required for hemagglutination, including five t hat encode prepilin or prepilin-like proteins, have been identified. Examin ation of MSHA-specific cDNAs has localized two promoters that drive express ion of these genes. This evidence indicates that the MSHA gene locus is tra nscriptionally organized into two operons, one encoding the secretory compo nents and the other encoding the structural subunits, an arrangement unique among previously characterized type 4 pilus loci. The genes flanking the M SHA locus encode proteins that show homology to YhdA and MreB of Escherichi a coli, In E. coil, the yhdA and mreB genes are adjacent to each other on t he chromosome. The finding that the MSHA locus lies between these two E, co li homologs and that it is flanked by a 7-bp direct repeat suggests that th e MSHA locus may have been acquired as a mobile genetic element.