DNA sequence polymorphisms in the genus Saccharomyces. V. Cloning and characterization of a LEU2 gene from S. carlsbergensis.

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 the LEU2 genes which encode the beta-isopropylmalate dehydrogenase and are located on chromosomes III. In the present work a LEU2 gene from S. carlsbergensis has been cloned and characterized. The cloned 2.6 kb LEU2 region complements the S. cerevisiae leu2-3 leu2-112 double mutation. The restriction endonuclease site map of the isolated S. carlsbergensis LEU2 gene is different from that of the S. cerevisiae LEU2 gene. Electrophoretic chromosome separation, as well as karl mediated transfer of single chromosomes into S. cerevisiae strains, has shown that the S. carlsbergensis specific LEU2 gene is located on a chromosome III which carries the carlsbergensis specific HIS4 gene. The cloned LEU2 gene shows preferential molecular hybridization to one of the two LEU2 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.