Abstract

TfoX (Sxy) and CRP are two important competence activators. The link between tfoX and CRP has been shown in H. influenza but lacking evidence of direct interaction. Recently a Sxy-dependent CRP (CRP-S) site autoregulating Sxy was reported in E. coli . Here, we show that the cAMP-CRP complex transcriptionally regulates tfoX expression through multiple canonical CRP (CRP-N) sites in Vibrios. This conclusion is supported by an analysis of the tfoX mRNA levels and tfoX transcriptional reporter fusions. The reduced expression of tfoX VC was restored by trans-complementation of crp in ∆ crp and by exogenous cAMP in ∆ cya . A promoter deletion analysis and the site-directed mutagenesis of the putative CRP-N sites revealed the presence of two functional CRP-N sites. The direct binding of cAMP-CRP to the tfoX VC promoter was demonstrated by EMSA assays. Additionally, the transcriptional start site (TSS) of tfoX VF in V. fluvialis was determined and −10/−35 regions were predicted. Further comparison of the tfoX promoter in Vibrios revealed the existence of similar −10 motifs and putative CRP-N sites, indicating the conserved mechanism of CRP regulation on tfoX . Our study demonstrates the direct binding of the cAMP-CRP complex to tfoX promoter and broadens the understanding of the molecular mechanism regulating tfoX in Vibrios .