POLYMORPHISM OF 2-MU-M PLASMIDS IN INDUSTRIAL STRAINS OF SACCHAROMYCES-CEREVISIAE

Restriction fragment length polymorphism (RFLP) analyses of industrial Saccharomyces yeast DNA have identified eight 2-mum plasmid variants that fall into two distinct types. Type-I plasmids are of unique form, whereas type-II plasmids exist in seven distinct RFLP forms. Only two different 2-mum variants were observed in 35 bakers' strains analysed . One variant was the unique type-I whereas the second variant represe nts an ancestral form of the type-II plasmid. Sixteen of nineteen wine yeasts carried a distinctive type-II plasmid with a homeologous STB r epeat whereas ale and lager yeasts had a wide range of type-II variant s. Relative to nuclear and mtDNA, 2-mum polymorphism is less diverse a nd not diagnostic for a specific strain. This 2-mum DNA polymorphism i s a convenient and useful addendum to nuclear and mtDNA RFLP analyses but cannot serve as the sole marker for strain identification. A tenta tive phylogeny of industrial S. cerevisiae yeasts is suggested with or igins in bakers' yeast carrying the ancestral type-II form.