MhbR, a LysR-type regulator involved in 3-hydroxybenzoate catabolism via gentisate in Klebsiella pneumoniae M5a1

SummaryIn Klebsiella pneumoniae M5a1, mhbTDHIM genes are involved in 3-hydroxybenzoate catabolism via the gentisate pathway. mhbR, which encodes a LysR-type transcriptional regulator, is divergently transcribed from the mhb structural genes. MhbR was found to be necessary for the expression of catabolic genes. Transcriptional studies demonstrated that the mhb structural genes are transcribed as an operon. The promoters of mhbR and the mhb operon are σ70-type and overlap with each other. 5′ Deletion analysis of the promoter transcription activity showed that a 233 bp fragment (position −144 to +89 according to the transcriptional start site of mhb operon) contained the element necessary for induction. β-Galactosidase activity assays and electrophoretic mobility shift assays showed that an inverted repeat sequence site 1 (ATAACCTCCAGGTTAT, position −70 to −55) within this fragment was critical for regulation.