A hybrid promoter and portable Shine-Dalgarno regions of Escherichia coli.

A gene expression system of Escherichia coli is described here that contains a portable Shine-Dalgarno region. Transcription of this system is under the direction of a hybrid promoter derived from trp and lac-UV5 promoter sequences which is followed by a region that encodes the portable Shine-Dalgarno (PSD) region. Using a series of synthetic PSD regions we varied the length (from 4 to 13 bases) of the Shine-Dalgarno region by increasing the number of bases on the mRNA that are complementary to the 3'-end of 16S rRNA. We found that increase of the Shine-Dalgarno region to 8 or 13 bases decreases the translation efficiency of the chimaeric leucocyte interferon messenger by 40%. We also varied in another series of PSD regions the four bases that follow the Shine-Dalgarno region. We found that the presence of four A residues or four T residues in this region results in the highest translation efficiency. The presence of four C residues reduces the translation efficiency by 50% as compared with PSD regions with A or T residues. The presence of four G residues following the Shine-Dalgarno region lowers the translation efficiency by 75% with respect to PSD regions with A or T residues.