COEXISTENCE OF 2 TYPES OF CHROMOSOME IN THE BOTTOM FERMENTING YEAST, SACCHAROMYCES-PASTORIANUS

The bottom fermenting yeasts in our collection were classified as Sacc haromyces pastorianus on the basis of their DNA relatedness. The genom ic organization of bottom fermenting yeast was analysed by Southern hy bridization using eleven genes on chromosome IV, six genes on chromoso me II and five genes on chromosome XV of S. cerevisiae as probes. Gene probes constructed from S. cerevisiae chromosomes II and TV hybridize d strongly to the 820-kb chromosome and the 1500-kb chromosome of the bottom fermenting yeast, respectively. Five gene probes constructed fr om segments of chromosome XV hybridized strongly to the 1050-kb and th e 1000-kb chromosomes. These chromosomes are thought to be S. cerevisi ae-type chromosomes. In addition, these probes also hybridized weakly to the 1100-kb, 1350-kb, 850-kb and 700-kb chromosome. Gene probes con structed from segments including the left arm to TRP1 of chromosome IV and the right arm of chromosome II hybridized to the 1100-kb chromoso me of S. pastorianus. Gene probes constructed using the right arm of c hromosome IV and the left arm of chromosome II hybridized to the 1350- kb chromosome of S. pastorianus. These results suggested that the 1100 -kb and 1350-kb chromosomes were generated by reciprocal translocation between chromosome II and IV in S. pastorianus. Three gene probes con structed using the right arm of chromosome XV hybridized weakly to the 850-kb chromosome, and two gene probes from the left arm hybridized w eakly to the 700-kb chromosome. These results suggested that chromosom e XV of S. cerevisiae was rearranged into the 850-kb and 700-kb chromo somes in S. pastorianus. These weak hybridization patterns were identi cal to those obtained with S. bayanus. Therefore, two types of chromos ome co-exist independently in bottom fermenting yeast: one set which o riginated from S. bayanus and another set from S. cerevisiae. This res ult supports the hypothesis that S. pastorianus is a hybrid of S. cere visiae and S. bayanus. (C) 1998 John Wiley & Sons, Ltd.