Microevolutionary changes and chromosomal translocations are more frequent at RPS loci in Candida dubliniensis than...

The Cd1 fingerprinting probe of Candida dubliniensis, which is extremely effective in identifying microevolutionary changes in infecting populations, generates hybridization patterns that are similar to those generated by the Candida albicans fingerprinting probe Ca3. Since Ca3 recognizes microevolutionary changes through the repeat sequence RPS, it was suggested that Cd1 also contains a RPS-like element. To test this possibility, the C. albicans RPS unit was used as a probe, and an RPS-like element, RPSd1, was cloned from C. dubliniensis. The sequence of RPSd1 was 76% homologous to that of the C. albicans RPS unit RPS620 and the organization, including the non-RPS 3' and 5' bordering sequences, was highly similar. This analysis revealed additional copies of the repeat extraalt element and short additional repeat (SAR) sequences in both RPSd1 and RPS620 not previously identified in the latter. This analysis has allowed us to develop a model of RPSd1 organization and to revise the model for RPS620 organization. An estimate of the average frequency of reorganization (duplication and deletion) per RPS unit in C. dubliniensis was similar to that for C. albicans, but the estimate of frequency of reorganization per C. dubliniensis genome was higher, most probably as a result of the higher estimated average number of RPS clusters in C. dubliniensis. These results demonstrate that the microevolutionary changes identified by the Cd1 fingerprinting probe are based on the reorganization of RPS-like elements and are, therefore, similar to the microevolutionary changes identified by the Ca3 probe of C. albicans. Linkage analysis of pairs of markers situated on either side of an RPS cluster on chromosome 7 further revealed frequent recombination between non-homologous chromosomes at the RPS cluster in C. dubliniensis strains, but not in C. albicans strains, suggesting that RPS clusters may function as recombination hot spots in C. dubliniensis.