ARTIFICIAL PROMOTERS FOR METABOLIC OPTIMIZATION

In this article, we review some of the expression systems that are ava ilable for Metabolic Control Analysis and Metabolic Engineering, and e xamine their advantages and disadvantages in different contexts. In a recent approach, artificial promoters for modulating gene expression i n micro-organisms were constructed using synthetic degenerated oligonu cleotides. From this work, a promoter library was obtained for Lactoco ccus lactis, containing numerous individual promoters and covering a w ide range of promoter activities. Importantly, the range of promoter a ctivities was covered in small steps of activity change. Promoter libr aries generated by this approach allow for optimization of gene expres sion and for experimental control analysis in a wide range of biologic al systems by choosing from the promoter library promoters giving, e.g ., 25%, 50%, 200%, and 400% of the normal expression level of the gene in question. If the relevant variable (e.g., the flux or yield) is th en measured with each of these constructs, then one can calculate the control coefficient and determine the optimal expression level. One ad vantage of the method is that the construct which is found to have the optimal expression level is then, in principle, ready for use in the industrial fermentation process; another advantage is that the system can be used to optimize the expression of different enzymes within the same cell. (C) 1998 John Wiley & Sons, Inc.