Portable Shine-Dalgarno regions; nucleotides between the Shine-Dalgarno sequence and the start codon affect the translation efficiency.

This chapter describes a gene expression system of E. coli that contains a portable Shine-Dalgarno region. Transcription of this system is directed by a hybrid promoter derived from trp and lac-UV5 promoter sequences, which is followed by a region that encodes the portable Shine-Dalgarno region. We used a series of synthetic portable Shine-Dalgarno regions to vary the length (from 4 to 13 bases) of the Shine-Dalgarno by increasing the number of bases on the mRNA that are complementary to the 3' end of 16s rRNA. Increase in the Shine-Dalgarno region to 8 or 13 bases decreased the translation efficiency of the chimeric leukocyte interferon messenger by 40%. In another series of portable Shine-Dalgarno regions, we varied the four bases that follow the Shine-Dalgarno region. The presence of four A residues or four T residues in this region resulted in the highest translation efficiency. The presence of four C residues reduced translation efficiency by 50%, compared with A or T residues. The presence of four G residues after the Shine-Dalgarno region lowered translation efficiency by 75%, compared with A or T residues.