A physical comparison of chromosome III in six strains of Saccharomyces cerevisiae

We have tested the clones used in the European Yeast Chromosome III Sequencing Programme for possible artefacts that might have been introduced during cloning or passage through Escherichia coli. Southern analysis was performed to compare the BamHI, EcoRI, HindIII and PstI restriction pattern for each clone with that of the corresponding locus on chromosome III in the parental yeast strain. In addition, further enzymes were used to compare the restriction maps of most clones with the map predicted by the nucleotide sequence (Oliver et al., 1992). Only four of 506 6‐bp restriction sites predicted by the sequence were not observed experimentally. No significant cloning artefacts appear to disrupt the published sequence of chromosome III. The restriction patterns of six yeast strains have also been compared. In addition to two previously identified sites of Ty integration on chromosome III (Warmington et al., 1986; Stucka et al., 1989; Newlon et al., 1991), a new polymorphic site involving Ty retrotransposition (the Far Right‐Arm transposition Hot‐Spot, FRAHS) has been identified close to CRY1. On the basis of simple restriction polymorphisms, the strains S288C, AB972 and W303‐1b are closely related, while XJ24‐24a and J178 are more distant relatives of S288C. A polyploid distillery yeast is heterozygous for many polymorphisms, particularly on the right arm of the chromosome.