PHYSICAL CHARACTERIZATION OF THE ESCHERICHIA-COLI-B GENE ENCODING NITROREDUCTASE AND ITS OVER-EXPRESSION IN ESCHERICHIA-COLI K12

The Escherichia coli B gene (nfnB) encoding nitroreductase has been cl oned in Escherichia coli K-12 and its nucleotide sequence determined. The translated amino acid sequence was found to share substantial iden tity (88.5%) with the equivalent proteins of Enterobacter cloacae and Salmonella typhimurium. When the structural gene was placed under the transcriptional control of either the trp or lac promoter, recombinant nitroreductase was accumulated to 33% and 25% of the cell's soluble p rotein, respectively. Substitution of the nfrB ribosome binding site w ith that of the E. coli lacZ gene reduced production levels of nitrore ductase. The sequenced region also contained two incomplete open readi ng frames of unknown function.