Identification of a Vibrio cholerae ToxR-activated gene (tagD) that is physically linked to the toxin-coregulated pilus (tcp) gene cluster.

The toxin-coregulated pilus (TCP)-encoding gene cluster (tcp) specifies a type-IV pilus that is a major colonization determinant of Vibrio cholerae. We have identified a gene 200 bp upstream from the tcp cluster that requires ToxR for expression. We have designated this gene tagD (ToxR-activated gene) and have shown that tagD is encoded on a 600-nt transcript. The deduced tagD product is a 164-amino-acid polypeptide (20 kDa). Interestingly, TagD shares a high degree of similarity to a protein of Streptococcus sanguis 12 that is thought to play a role in fimbriae synthesis or assembly. The high degree of similarity between tagD and the Ss 12 protein provides preliminary evidence that tagD represents an additional member of the tcp cluster.