1991 Volume 17 Issue 3 Pages 674-679
To apply genetically engineered yeast cells to practical processes for the production of useful compounds, the construction of vector plasmids having high stability and expressive selection markers in polyploid wild yeast cells is required. For this purpose, we selected an ethionine -resistance phenotype of a yeast Saccharomyces cerevisiae as a marker and constructed a vector plasmid pER 9 containing ethionine-resistance gene. The vector plasmid pER9 was 9.8 kb in length, a suitable size for manipulation, and had available cloning sites (Bam H I and SalI) for foreign DNAs. The plasmid was stably maintained in haploid yeast cells and almost all the cells (98%) contained the plasmid, even after 40 generations, when ethionine was in the growth medium as a selection pressure. Since the ethionine-resistance gene on plasmid pER9 could be expressed and maintained in cells of yeast strains such as sake and beer yeasts, pER9 would make it possible to breed industrially useful polyploid strains of yeats at the molecular level.
