COPY NUMBER MODULATION IN AN AUTOSELECTION SYSTEM FOR STABLE PLASMID MAINTENANCE IN SACCHAROMYCES-CEREVISIAE

Efficient expression of a foreign gene requires a stable vector presen t at a high number of copies per cell. We have constructed an autosele ction system for the stable maintenance of expression vector in the ye ast Saccharomyces cerevisiae that uses the fructose 1,6-bisphosphate a ldolase gene (FBA1) to stabilize plasmids in cells bearing a disruptio n of the chromosomal FBA1 gene. This system allowed us to obtain stabl e production of a reporter heterologous enzyme (Escherichia coli beta- galactosidase) in rich media. By using an inducible promoter to regula te the expression of FBA1 gene, we have also obtained the modulation o f plasmid copy number by carbon source.