Clp upregulates transcription of engA gene encoding a virulence factor in Xanthomonas campestris by direct binding to the upstream tandem Clp sites.
In Xanthomonas campestris, the causative agent of black rot in crucifers, the endoglucanase level is greatly decreased in the mutant deficient in Clp, a homologue of cyclic AMP receptor protein (CRP). It is established that Clp has the same DNA binding specificity as CRP at positions 5, 6, and 7 (GTG motif) of the DNA half site. In this study, the engA transcription initiation site was determined by the 5' RACE method, and two consensus Clp-binding sites, site I and site II centered at -69.5 and -42.5, respectively, were located. Transcriptional fusion assays indicated that Clp greatly activates engA transcription. Site-directed mutagenesis indicated that position 5 of GTG motif in site II is essential for both DNA-protein complex formation in electrophoretic mobility shift assays and engA transcription in vivo. In addition, mutation at position 5 of site I drastically reduces the promoter activity, indicating that binding of Clp to site I exerts a synergistic effect on the transcription activation by site II. engA appears to be the first X. campestris gene known to be activated by Clp via a direct binding to the promoter.
Hsiao
Yi-Min
YM
Institute of Medical Biotechnology, Chungtai Institute of Health Sciences and Technology, Taichung 406, Taiwan, ROC.
Liao
Hsiu-Ying
HY
Lee
Mong-Chuan
MC
Yang
Tsuey-Ching
TC
Tseng
Yi-Hsiung
YH
D001426:Bacterial Proteins; D001483:Base Sequence; D001665:Binding Sites; D002373:Cyclic AMP Receptor Protein / Q000378:metabolism; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D011401:Promoter Regions, Genetic; D014157:Transcription Factors / Q000378:metabolism*; D024363:Transcription Initiation Site; D015533:Transcriptional Activation; D015854:Up-Regulation; D037521:Virulence Factors / Q000235:genetics*; D016959:Xanthomonas campestris / Q000235:genetics* / Q000472:pathogenicity
D001426:Bacterial Proteins; C436751:Clp protein, Xanthomonas campestris; D002373:Cyclic AMP Receptor Protein; D014157:Transcription Factors; D037521:Virulence Factors