Pseudomonas pseudoalcaligenes KF707 possesses a chromosomally encoded bph gene cluster responsible for the catabolism of biphenyl/polychlorinated biphenyls. The gene cluster consists of (orf0)bphA1A-2(orf3)bphA3A4BCX0X1X2X3D. We studied the role of orf0 and transcription in the KF707 bph operon. Primer extension analyses revealed that at least as many as six transcriptional initiation sites exist upstream of orf0, bphA1, bphX0, bphX1, and bphD, including two upstream of bphD. The orf0-disruptant failed to grow on biphenyl but accumulated large amounts of the biphenyl ring meta-cleavage yellow compound (2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoate). Western blot analysis revealed that ORF0 protein is inducibly expressed in KF707 in the presence of biphenyl. Gel shift assay revealed that ORF0 directly binds to the orf0 operator region. This binding was greatly enhanced by addition of the biphenyl ring meta-cleavage yellow compound. These results indicated that orf0, bphA1A2(orf3)bphA3A-4BC and bphX0X1X2X3D are independently transcribed, and that ORF0 protein belonging to the GntR family is involved in the regulation of the bph operon in KF707 and is absolutely required for the expression of orf0 and bphX0X1X2X3D.

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