Structural characterization of chromosome I size variants from a natural yeast strain

Many yeast strains isolated from the wild show karyotype instability during growth, with rearrangement rates of up to 10(-2) chromosomal changes per Physical isolation and analysis of several chromosome I size variants of one these strains revealed that they differed only in their subtelomeric regions, the central 150 Kb unaltered. Fine mapping of these subtelomeric variable revealed gross alterations of two very similar loci, FLO1 and FLO9. These loci located on the right and left arms, respectively, of chromosome I and internal repetitive DNA sequences. Furthermore, some chromosome I variants the FLO1 locus showed evidence of recombination at a DNA region on their arm that is enriched in repeated sequences, including Ty LTRs. We propose repetitive sequences in many subtellomeric regions in S. cerevisiae play a key in karyotype hypervariability. As these regions encode several proteins, subtelorneric plasticity may allow rapid adaptive changes of the yeast to specific substrates. This pattern of semi-conservative chromosomal may have profound implications, both in terms of evolution of wild strains and biotechnological processes. Copyright (C) 2002 John Wiley Sons, Ltd.