AbstractEfficient expression of a foreign gene requires a stable vector present at a high number of copies per cell. We have constructed an autoselection system for the stable maintenance of expression vector in the yeastSaccharomyces cerevisiaethat uses the fructose 1, 6‐bisphosphate aldolase gene (FBA1) to stabilize plasmids in cells bearing a disruption of the chromosomalFBA1gene. This system allowed us to obtain stable production of a reporter heterologous enzyme (Escherichia coli β‐galactosidase) in rich media. By using an inducible promoter to regulate the expression ofFBA1gene, we have also obtained the modulation of plasmid copy number by carbon so
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