An L-arabinose-inducible T7 expression system was shown to be highly stringent in the regulation of cloned gene expression. However, this stringency was medium-dependent and missing in complex media. To ensure consistent expression efficiency, the system was improved by constructing T7lac promoter-containing plasmids subject to the control of thermo-labile lacI. As a result, LacZ was produced to reach a 128-fold increase over the uninduced level in rich media. Furthermore, a large production of carbamoylase using the developed system was successfully achieved in a lab-scale fermenter. The production of soluble protein was 10% of total cell protein content and the cell yield 30 g dry cell weight per litre. Taken together, these illustrate the great promise of this system for industrial use. (c) 2005 Elsevier Ltd. All rights reserved.