FIG 6.

Model illustrating the interactions between the Pho regulon, yaiC, and type 1 fimbriae. Arrows represent an activation/promotion, while ⊥ represents an inhibition. The induction of PhoBR leads to transcription of yaiC from the promoter of phoA, which leads to the biosynthesis of c-di-GMP, repression of ipuA and ipbA, and then reduced expression of the fim operon by promoting the off orientation of fimS. It is not known (question mark on the right) whether c-di-GMP directly or indirectly inhibits the expression of ipuA and ipbA. Furthermore, c-di-GMP could inhibit the recombinase activity instead of its transcription. As for ipuA and ipbA, it is not known (question mark on the left) whether c-di-GMP directly or indirectly affects FimB or fimB.