CONSERVATION OF CIS-ACTING ELEMENTS WITHIN THE TOR REGULATORY REGION AMONG DIFFERENT ENTEROBACTERIACEAE

The Escherichia coli (Ec) torCAD operon encoding the trimethyl amine N -oxide (TMAO) reductase system is induced by both TMAO and anaerobiosi s. The tor regulatory regions from bacteria related to Ec have been am plified by the polymerase chain reaction (PCR) using degenerate oligod eoxyribonucleotide primers based on conserved sequences of the tor pro ducts. The amplified regions from Salmonella enteritidis and Sa. typhi murium (St) were the same size as that from Ec and showed 82% identity with it, Interestingly, four boxes of a 10-nucleotide motif (5'-CTGTT CATAT) were found in direct repeat at the same location in the tor. re gulatory region of the three species. Although the amplified fragment from Shigella sonnei (Ss) was highly homologous to the Ec correspondin g segment, the first tor box was missing, In Ec, the St and Ss tor pro moters were still regulated by both TMAO and anaerobiosis, but their t ranscriptional activities were significantly lower than that of the Ec tor promoter. Deletion of the two first boxes of the Ec tor regulator y region inactivated the tor promoter while deletion of the region jus t upstream from the tor boxes led to a significant decrease in tor exp ression. Our results strongly suggest that the tor boxes, as well as s pecific sequences outside the tor boxes, play an important role in the expression of the tor operon.