CHROMOSOME POLYMORPHISMS CLOSE TO THE CM-ADE1 LOCUS OF CANDIDA-MALTOSA

The imperfect yeast Candida maltosa has an ill-defined genetic constit ution; it is nominally diploid, but probably highly aneuploid, in natu re. We report on polymorphisms specifically affecting those chromosome s which bear the cm-ADE1 gene. This gene encodes phosphoribosylaminoim idazole-succino-carboxamide synthetase, an enzyme in the adenine biosy nthetic pathway. By electrophoretic karyotype analysis, three differen tly sized chromosomes were demonstrated to carry cm-ADE1; the size (bu t not the number) of these chromosomes was also found to vary, both be tween strains and during the mitotic growth of a single strain. Four d ifferent alleles of cm-ADE1 have been cloned and sequenced from one pr ototrophic strain. DNA sequence divergence between these different all eles is as high as 8%, with the greatest divergence being found in the upstream region. Mitotic recombination events that led to changes in the karyotype were followed by using cm-ADE1 DNA as an hybridization p robe. A recombination hot-spot in the neighbourhood of the gene appear s to be responsible for the instability of the chromosomes on which it resides.