THE PERIPLASMIC TORT PROTEIN IS REQUIRED FOR TRIMETHYLAMINE N-OXIDE REDUCTASE GENE INDUCTION IN ESCHERICHIA-COLI

Expression of the Escherichia coli torCAD operon, which encodes the tr imethylamine N-oxide reductase system, is regulated by the presence of trimethylamine N-oxide through the action of the TorR response regula tor. We have identified an additional gene, torT, located just downstr eam from the torR gene, which is necessary for torCAD structural opero n expression. Insertion within the torT gene dramatically reduced the expression of a torA'-'lacZ fusion, while presence of the gene in tran s restored the wild-type phenotype. Overproduction of TorR in a torT s train resulted in partial constitutive expression of the torA'-'lacZ f usion, suggesting that TorR acts downstream from TorT. The torT gene c odes for a 35.7-kDa periplasmic protein which presents some homology w ith the periplasmic ribose-binding protein of E. coli. We discuss the possible role of TorT as an inducer-binding protein involved in signal transduction of the tor regulatory pathway.