Genomic structure of Candida stellatoidea: extra chromosomes and gene duplication

Candida albicans and Candida stellatoidea are two closely related imperfect yeasts. Some isolates characterized as C. stellatoidea are in fact C. albicans, while others differ with respect to virulence and to karyotype, containing extra small chromosomes. Experiments in this study allowed us to infer that a typical C. stellatoidea isolate, Y2360, has 12 chromosomes rather than the 7 previously shown for C. albicans. The majority of cloned sequences tested hybridized to analogous chromosomes in C. albicans and in C. stellatoidea, although there were exceptions, and a repeated element isolated as specific for C. albicans hybridized to most of the chromosomes of C. stellatoidea. Several genes tested hybridized to one of the smaller, C. stellatoidea-specific chromosomes as well as to a larger one. The arrangement of restriction enzyme sites around the gene was the same in both the large and small chromosomes. For ADE2 and LYS2, the arrangements were identical to those of a typical C. albicans strain, FC18, suggesting a high degree of sequence conservation between the two species. Spheroplast fusion and segregation experiments showed that the ADE2 genes on both the large and small chromosomes of C. stellatoidea are active, implying that the organism is functionally at least triploid for this gene and probably for any others duplicated on the smaller chromosomes.