Clonal variation of chromosome size derived from the rDNA cluster region in Candida albicans

Of the eight Candida albicans chromosomes, chromosome 2, assigned by the MGL1 probe, is more variable in size than the other chromosomes among strains. We found that the clonal variation of chromosome 2, which carries a rDNA gene, occurred at a frequency of up to 10% of the progeny clones. After total chromosomal digestion with XhoI, which has no recognition sites within the rDNA repeat unit, the fragments containing the rDNA cluster were detected by Southern hybridization. The difference in fragment sizes corresponded to the clonal size variation of chromosome 2. The intensity of hybridization with rDNA also correlated with the difference in size. In addition, there was no size change in the non-rDNA region as detected by NotI digestion of chromosome 2, and there was no observed change in the individual rDNA basic repeat unit size. From these lines of evidence, we confirmed that the clonal size variation of chromosome 2 which occurs at high frequency is derived from the size change of the rDNA cluster.