FIG 9.

Model for the interplay between NanI, CodY, and CcpA in the regulation of codY and etx. (A) MEME analysis was performed using regions upstream of the ccpA, codY, and etx genes, as well as predicted CcpA-binding cre sites of C. perfringens, in order to identify an overall C. perfringens cre site motif consensus sequence and putative cre sites upstream of these genes. (B) Parallel MEME analysis was performed using the region upstream of the etx gene and putative CodY-binding sites from C. difficile in order to identify putative CodY-binding sites upstream of etx. Each putative cre box or CodY-binding site is shown, along with the distance upstream of the etx or codY ATG start codon and a P value corresponding to the strength of consensus matching. (C) Model for NanI induction of ETX production. See the text in Discussion for an explanation. Note that steps up to the generation of sialic acid by NanI occur extracellularly, but the remainder of the model involves intracellular events. Red boxes depict putative cre sites, while blue boxes indicate putative CodY binding sites. The question marks indicate other potential, but unknown, regulators of codY or ccpA transcription.