A novel sequence element derived from bacteriophage T7 mRNA acts as an enhancer of translation of the lacZ gene in Escherichia coli

We recently reported that a ribosome binding site (RBS) derived from gene 10 of bacteriophage T7 (g10-L) causes a pronounced stimulation of expression when placed upstream of a variety of genes, and that this effect is probably due to a stimulation of translation efficiency in Escherichia coli (Olins, P. O., Devine, C. S., Rangwala, S. H., Kavka, K. S. (1988) Gene (Amst.) 73, 227-235). Here we present a model for the mechanism of action of the g10-L: the RBS contains a 9-base sequence which has the potential for forming a novel base-paired interaction with bases 458-466 of the 16 S rRNA of E. coli. Although such sequence homologies are rare in E. coli RBS regions, a number of similar sequences were found in the RBS regions of other bacteriophage structural genes. When an isolated homology sequence was placed upstream of a synthetic RBS, there was a 110-fold increase in the translation efficiency of the lacZ gene. Surprisingly, the homology sequence also stimulated translation when placed downstream of the initiator codon, indicating that this sequence is acting as a translational "enhancer."