THE TOPOISOMERASE-I GENE FROM CANDIDA-ALBICANS

We report here the cloning of the Candida albicans genomic topoisomera se I gene (TOP1) by use of PCR and subsequent hybridization. The predi cted protein sequence shared 58.8 % identity with the Saccharomyces ce revisiae topoisomerase I and 30-50 % identity with other eukaryotic to poisomerase I proteins. A conditional gene disruption strain (CWJ477) was constructed so that one copy of TOP1 was deleted and the other cop y of TOPI was placed under a regulatable promoter. Under repressed con ditions, cells grew slowly and cell morphology was abnormal. The virul ence of CWJ477 was markedly reduced in a mouse model system, and that of the single gene knockout strain was slightly attenuated, indicating that TOP1 might play a role in the infection of C. albicans in mice i n a dose-dependent manner. Despite the reduced virulence of both the s ingle and double knockout strains, viable cells of the pathogen were r ecovered from the kidneys as late as 22 d post-infection.