Curing of Saccharomyces cerevisiae 2-μm DNA by transformation.

A general procedure for the curing of 2-μm in Saccharomyces cerevisiae is described. The method is based on the displacement of endogenous 2-μm DNA by the recombinant plasmid pMP78-1, which carries the yeast leu2 gene and the 2 -μm DNA replicon, but cannot be maintained stably in a yeast cell without endogenous 2-μm DNA. After transformation with pMP78-1 cells are grown selectively to displace 2-μm DNA. During the non-selective growth which follows, plasmid pMP78-1 is lost and up to 100% of the cells completely lack plasmids. In conjunction with a kanamycin resistance marker, as present in plasmid pMP81, this method should be applicable to cure any wild-type yeast strain. The stability of recombinant plasmids in cir (+) and cir (0) strains has been compared.