G. Simon et al., THE TORR GENE OF ESCHERICHIA-COLI ENCODES A RESPONSE REGULATOR PROTEIN INVOLVED IN THE EXPRESSION OF THE TRIMETHYLAMINE N-OXIDE REDUCTASE GENES, Journal of bacteriology, 176(18), 1994, pp. 5601-5606
Expression of the Escherichia coli torCAD operon encoding the trimethy
lamine N-oxide (TMAO) reductase system is induced by both TMAO and ana
erobiosis. A torR insertion mutant unable to express the torA gene had
previously been isolated. The torR gene was cloned and sequenced. It
encodes a 25,000-Da protein which shares homology with response regula
tors of two-component systems and belongs to the OmpR-PhoB subclass. O
verproduction of TorR mimicks the presence of the inducer TMAO while t
he anaerobic control is unchanged, suggesting that TorR mediates only
the TMAO induction. The overproduced TorR protein was purified to more
than 90%. The torR gene is located just upstream of the torCAD operon
, with an opposite transcription direction. The torR-torCAD intergenic
region is unusual in that it contains four direct repeats of a 10-nuc
leotide motif. Part or all of these motifs could be involved in the bi
nding of TorR. The gene encoding the sensor partner does not seem to b
e adjacent to torR, since the divergent open reading frame found immed
iately downstream of torR exhibits none of the features of a protein h
istidine kinase.