DNA sequence polymorphisms in the genus Saccharomyces. V. Cloning and characterization of aLEU2 gene from S. carlsbergensis

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Abstract
Saccharomyces carlsbergensis strains used in the production of lager beer are structurally heterozygous in most genetic loci studied to date. Previous studies have shown that the genotype of lager yeast contains two types of genomes, one of which is derived from S. cerevisiae and the other reveals similarities to the genomes of S. bayanus and S. monacensis. Genes of homeologous chromosomes can be distinguished by characteristic restriction fragment patterns. This is true also for theLEU2 genes which encode the β-isopropylmalate dehydrogenase and are located on chromosomes III. In the present work aLEU2 gene from S. carlsbergensis has been cloned and characterized. The cloned 2.6 kbLEU2 region complements the S. cerevisiaeleu2-3 Ieu2-112 double mutation. The restriction endonuclease site map of the isolated S. carlsbergensisLEU2 gene is different from that of the S. cerevisiaeLEU2 gene. Electrophoretic chromosome separation, as well askarl mediated transfer of single chromosomes into S. cerevisiae strains, has shown that the S. carlsbergensis specificLEU2 gene is located on a chromosome III which carries the carlsbergensis specificHIS4 gene. The clonedLEU2 gene shows preferential molecular hybridization to one of the twoLEU2 structural alleles present in lager strains, an allele which is also present in type strains of S. bayanus, S. carlsbergensis, S. monacensis and S. uvarum.