| Summary: | <p>Abstract</p> <p>Background</p> <p>Pathogenic yersiniae, including <it>Y. pestis</it>, share a type III secretion system (T3SS) that is composed of a secretion machinery, a set of translocation proteins, a control system, and six Yop effector proteins including YpkA and YopJ. The cyclic AMP receptor protein (CRP), a global regulator, was recently found to regulate the laterally acquired genes (<it>pla </it>and <it>pst</it>) in <it>Y. pestis</it>. The regulation of T3SS components by CRP is unknown.</p> <p>Results</p> <p>The <it>sycO</it>, <it>ypkA </it>and <it>yopJ </it>genes constitute a single operon in <it>Y. pestis</it>. CRP specifically binds to the promoter-proximate region of <it>sycO</it>, and represses the expression of the <it>sycO-ypkA-yopJ </it>operon. A single CRP-dependent promoter is employed for the <it>sycO-ypkA-yopJ </it>operon, but two CRP binding sites (site 1 and site 2) are detected within the promoter region. A CRP box homologue is found in site 1 other than site 2. The determination of CRP-binding sites, transcription start site and core promoter element (-10 and -35 regions) promotes us to depict the structural organization of CRP-dependent promoter, giving a map of CRP-promoter DNA interaction for <it>sycO-ypkA-yopJ</it>.</p> <p>Conclusion</p> <p>The <it>sycO-ypkA-yopJ </it>operon is under the direct and negative regulation of CRP in <it>Y. pestis</it>. The <it>sycO-ypkA-yopJ </it>promoter-proximate regions are extremely conserved in <it>Y. pestis</it>, <it>Y. pseudotuberculosis </it>and <it>Y. enterocolitica</it>. Therefore, data presented here can be generally applied to the above three pathogenic yersiniae.</p>
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