3901-3905 , June 1987 Microbiology The narL gene product activates the nitrate reductase operon and represses the fumarate reductase and trimethylamine N-oxide reductase operons in Escherichia coli ( frd gene/tor gene/regulation ) S. Thus the D3 region is not apparently required for NanR to activate fimB expression in the wildtype background , and it could contain specific sequences that inhibit this .