Genetic differences between Saccharomyces carlsbergensis and S. cerevisiae. Analysis of chromosome III by single chromosome transfer

Abstract

Tetrad analysis of most Saccharomyces strains used in beer production is impossible due to a low yield of viable spores. The present paper describes the use of single chromosome transfer in the genetic analysis of a brewer's yeast. The technique employs the kar1 mutation, which reduces karyogamy after conjugation. In rare cases karl×KAR crosses yield progeny resulting from the transfer of one chromosome or a limited number of chromosomes from a nucleus of one parent to one of the other. S. cerevisiae strains with an extra S. carlsbergensis chromosome III have thus been isolated from crosses between spore derived clones of the brewing strain and haploid kar1 S. cerevisiae strains carrying several auxotrophic markers. When the disomics were crossed to other haploid S. cerevisiae strains a normal spore viability was obtained, allowing tetrad analysis. High functional homology was found between the transferred S. carlsbergensis chromosome and chromosome III of S. cerevisiae. All genes essential for viability on the latter are represented on the former as are also HIS4, LEU2, MAT and THR4. Despite the functional homology, the transferred chromosome had a structure that was substantially different from that of standard S. cerevisiae strains. It did not recombine with S. cerevisiae chromosomes III, except in a certain region, where recombination was normal. Furthermore, restriction endonuclease analysis showed that the variant chromosome has a nucleotide sequence in the HIS4 region different from that of S. cerevisiae. The S. carlsbergensis brewing strain is heterozygous for this sequence variation, containing also a HIS4 region with a sequence identical or close to that of S. cerevisiae. © 1981 Carlsberg Laboratory.