The loss of parts of chromosome 7 followed by the insertion ofURAcassette into RB2 on MRS inCandida albicansstrain CAI-4

Abstract

Clinical isolates of the medically important fungus Candida albicans show electrophoretic karyotype variations. Chromosome translocation is considered to be one of the possible mechanisms of karyotype variation and has been shown to occur very frequently at or near the unique repeated DNA sequences which comprise the Major Repeat Sequence (MRS) on the genome. The MRS consists of the repeated sequences RB2, RPS, and HOK. We previously showed the insertion at the RB2 region might initiate chromosome translocation in strain STN22u2 of C. albicans. To ask whether the insertion of a URA cassette into the RB2 but not into RPS and HOK causes chromosome translocation in C. albicans strains, we transformed three URA cassettes into strain CAI-4, which is commonly used as a host strain for gene knockout experiments. We found chromosome rearrangements followed the insertion of URA cassettes into RB2 in strain CAI-4. Three transformants had an extra chromosome showing the loss of the 7A and 7C region from one chromosome 7 homologue. The recombination occurred at or after the insertion of URA cassette into RB2. Insertion there seems to cause chromosome rearrangement and thus RB2 is considered one of the important elements for initiation of chromosome rearrangement.