ABSTRACT A series of new expression vectors (pPro) have been constructed for the regulated expression of genes in Escherichia coli . The pPro vectors contain the prpBCDE promoter (P prpB ) responsible for expression of the propionate catabolic genes ( prpBCDE ) and prpR encoding the positive regulator of this promoter. The efficiency and regulatory properties of the prpR -P prpB system were measured by placing the gene encoding the green fluorescent protein ( gfp ) under the control of the inducible P prpB of E. coli . This system provides homogenous expression in individual cells, highly regulatable expression over a wide range of propionate concentrations, and strong expression (maximal 1,500-fold induction) at high propionate concentrations. Since the prpBCDE promoter has CAP-dependent activation, the prpR -P prpB system exhibited negligible basal expression by addition of glucose to the medium.
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