MdoR Is a Novel Positive Transcriptional Regulator for the Oxidation of Methanol in Mycobacterium sp Strain JC1

Mycobacterium sp. strain JC1 is able to grow on methanol as a sole source of carbon and energy using methanol:N,N'-dimethyl-4-nitrosoaniline oxidoreductase (MDO) as a key enzyme for methanol oxidation. The second open reading frame (mdoR) upstream of, and running divergently from, the mdo gene was identified as a gene for a TetR family transcriptional regulator. The N-terminal region of MdoR contained a helix-turn-helix DNA-binding motif. An electrophoretic mobility shift assay (EMSA) indicated that MdoR could bind to a mdo promoter region containing an inverted repeat. The mdoR deletion mutant did not grow on methanol, but growth on methanol was restored by a plasmid containing an intact mdoR gene. In DNase I footprinting and EMSA experiments, MdoR bound to two inverted repeats in the putative mdoR promoter region. Reverse transcription-PCR indicated that the mdoR gene was transcribed only in cells growing on methanol, whereas beta-galactosidase assays showed that the mdoR promoter was activated in the presence of methanol. These results indicate that MdoR serves as a transcriptional activator for the expression of mdo and its own gene. Also, MdoR is the first discovered member of the TetR family of transcriptional regulators to be involved in the regulation of the methanol oxidation, as well as to function as a positive autoregulator.