A GntR-like negative regulator of the biphenyl degradation genes of the transposon Tn4371.

Tn4371, a 55-kb catabolic transposon originally isolated from Ralstonia eutropha A5, carries genes for the degradation of biphenyl/4-chlorobiphenyl, which are clustered on a 13-kb DNA segment located in the middle of the element. DNA sequencing revealed that two potential regulatory genes, bphR and bphS, border this region. Transcriptional fusion experiments using bphC as a reporter gene, Northern hybridization and primer extension analysis led to the conclusion that the transposon-encoded genes bphEFGA1A2A3BCD form an operon transcribed from a sigma70 promoter, pE. Transcription from pE was not influenced by deletion of the bphR gene of Tn4371, which should encode a LysR-like regulator. The bphS gene product negatively regulated pE, and displayed significant similarity to GntR-like regulators. This is the first reported example of a GntR-like regulator involved in the control of an aromatic degradation pathway.