Transcription factor CecR (YbiH) regulates a set of genes affecting the sensitivity of Escherichia coli against cefoperazone and chloramphenicol.

Genomic SELEX (systematic evolution of ligands by exponential enrichment) screening was performed for identification of the binding site of YbiH, an as yet uncharacterized TetR-family transcription factor, on the Escherichia coli genome. YbiH was found to be a unique single-target regulator that binds in vitro within the intergenic spacer located between the divergently transcribed ybiH-ybhGFSR and rhlE operons. YbhG is an inner membrane protein and YbhFSR forms a membrane-associated ATP-binding cassette (ABC) transporter while RhlE is a ribosome-associated RNA helicase. Gel shift assay and DNase footprinting analyses indicated one clear binding site of YbiH, including a complete palindromic sequence of AATTAGTT-AACTAATT. An in vivo reporter assay indicated repression of the ybiH operon and activation of the rhlE operon by YbiH. After phenotype microarray screening, YbiH was indicated to confer resistance to chloramphenicol and cefazoline (a first-generation cephalosporin). A systematic survey of the participation of each of the predicted YbiH-regulated genes in the antibiotic sensitivity indicated involvement of the YbhFSR ABC-type transporter in the sensitivity to cefoperazone (a third-generation cephalosporin) and of the membrane protein YbhG in the control of sensitivity to chloramphenicol. Taken together with the growth test in the presence of these two antibiotics and in vitro transcription assay, it was concluded that the hitherto uncharacterized YbiH regulates transcription of both the bidirectional transcription units, the ybiH-ybhGFSR operon and the rhlE gene, which altogether are involved in the control of sensitivity to cefoperazone and chloramphenicol. We thus propose to rename YbiH as CecR (regulator of cefoperazone and chloramphenicol sensitivity).

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