Two yeast isolates, a wine-making yeast first identified as a Mel+ strain (ex. S. uvarum) and a cider-making yeast, were characterized for their nuclear and mitochondrial genomes. Electrophoretic karyotyping analyses, restriction fragment length polymorphism maps of PCR-amplified MET2 gene fragments, and the sequence analysis of a part of the two MET2 gene alleles found support the notion that these two strains constitute hybrids between Saccharomyces cerevisiae andSaccharomyces bayanus. The two hybrid strains had completely different restriction patterns of mitochondrial DNA as well as different sequences of the OLI1 gene. The sequence of the OLI1 gene from the wine hybrid strain appeared to be the same as that of the S. cerevisiae gene, whereas theOLI1 gene of the cider hybrid strain is equally divergent from both putative parents, S. bayanus and S. cerevisiae. Some fermentative properties were also examined, and one phenotype was found to reflect the hybrid nature of these two strains. The origin and nature of such hybridization events are discussed.

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Using genetic hybridization analysis, pulsed-field gel electrophoresis of chromosomal DNA and PCR/RFLP analysis of the MET2 gene, we reidentified 11 Champagne yeast strains. Two of them, SCPP and SC4, were found to belong to Saccharomyces bayanus var. uvarum and the remaining strains to S. cerevisiae. Strain