A library of synthetic promoters for Lactococcus lactis was constructed, in which the known consensus sequences were kept constant while the sequences of the separating spacers were randomized. The library consists of 38 promoters which differ in strength from 0.3 relative units, and up to more than 2000 relative units, which is among the strongest promoters known for this organism. The ranking of the promoter activities was somewhat different when assayed in E. coli, but the promoters are efficient for modulating gene expression in this bacteria as well. DNA sequencing revealed that the weaker promoters (which had activities below 5 relative units) all had either changes in the consensus sequences or in the length of the spacer between the -35 and -10 sequences. The promoters in which those features were conserved had activities from 5 to 2050 units, which shows that by randomizing the spacers, at least a 400 fold change in activity can be obtained. Interestingly, the entire range of promoter activities is covered in small steps of activity increase, which makes these promoters very suitable for quantitative physiological studies and for fine tuning of gene expression in industrial bio-reactors and cell factories.
Applied and Environemental Microbiology, 1998, Vol 64, Issue 1, p. 82-87