A loop-controlled rrnB P1 promoter for high-level expression of heterologous proteins in Escherichia coli

An effective protein expression system was constructed in Escherichia coli utilizing the rRNA rrnB P1 promoter and the regulatory element of the lac operon (lacO). To regulate the transcriptional activity of the rrnB P1 promoter, we designed two lacO sites with an intervening loop structure; expression was verified by measuring the levels of the beta-1,4-glucanase gene, cel5G. Basal expression from the looped promoter construct was reduced by 92% when compared to expression from the T7 promoter. We also found that the host cell type had a significant effect on the regulation of the rrnB P1 promoter: E. coli DH5 alpha and DH10B had high expression levels, whereas the expression in BL21(DE3) was more stringent.