FIG. 1.

Genomic organization of the pTLC (TLC) element, the CTX prophage, and the RTX gene cluster on the V. cholerae chromosome. The pTLC element is 842 bp upstream of the CTX element whereas the RTX gene cluster is 693 bp downstream of the CTX element. Open and filled boxes represent ORFs that are oriented left to right and right to left, respectively. The pTLC element is tandemly duplicated on the chromosome. In El Tor strains, the first copy contains an insertion sequence that shares sequence similarity to IS911. The CTX prophage is also commonly tandemly duplicated in toxigenic strains. In classical strains, the RTX gene cluster is disrupted by a deletion that removes part of rtxA and rtxB and all of rtxC.