Dissolved oxygen (DO)-controlled nor promoter expression vectors were constructed, and their expression efficiency was compared with that of the T7 promoter pET22 expression vector by expressing human growth hormone (hGH), enhanced green fluorescence protein (EGFP), and beta-tyrosinase in Escherichia coil cells. The nor promoter expression vector pRBS, which was engineered with a 5'-untranslated region and ribosomal binding site for the T7 promoter, expressed hGH at a rate of up to 32% of the total cellular proteins (TCP) in E. coil W3110narL(-). The expression level of hGH was further enhanced, up to similar to 42% of the TCP, by adding the N-terminal peptide tag of beta-galactosidase to hGH, which was comparable to the expression of similar to 43% of the TCP in pET-lac:hGH/BL21(DE3). A further engineered expression vector, pRBS(fnr), which coexpressed fumarate/nitrate reductase (fnr), expressed more EGFP than pET22 in BL21(DE3). In addition, recombinant beta-tyrosinase was successfully expressed at a rate of up to similar to 45% of the TCP in pRBS(fnr) in W3110narL-. From these results, the DO-controlled nor promoter system developed in this study can be considered a reliable and cost-effective expression system for protein production, especially in large-scale fermentation, as an alternative to the pET/BL(DE3) system. (C) 2010 Elsevier B.V. All rights reserved.