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 El Tor biotype is a member of the family of type 4 pili. Type 4 pili are found on the surface of a variety of gram-negative bacteria and have demonstrated importance as host colonization factors, bacteriophage receptors, and mediators 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. cholerae chromosome. Sixteen genes required for hemagglutination, including five that encode prepilin or prepilin-like proteins, have been identified. Examination of MSHA-specific cDNAs has localized two promoters that drive expression of these genes. This evidence indicates that the MSHA gene locus is transcriptionally organized into two operons, one encoding the secretory components and the other encoding the structural subunits, an arrangement unique among previously characterized type 4 pilus loci. The genes flanking the MSHA locus encode proteins that show homology to YhdA and MreB of Escherichia coli. In E. coli, the yhdA and mreB genes are adjacent to each other on the chromosome. The finding that the MSHA locus lies between these two E. coli homologs and that it is flanked by a 7-bp direct repeat suggests that the MSHA locus may have been acquired as a mobile genetic element.