Functional Characterization Of Genes Related To Target Of Rapamycin (TOR) Signaling In Candida Albicans And Saccharomyces Cerevisiae

The action of protein kinase TOR (Target of Rapamycin) is conserved from yeasts to mammals. TOR exists in the forms of two functionally distinct complexes, TOR complex 1 (TORC1) and TOR complex 2 (TORC2), in Saccharomyces cerevisiae. There are two interruptions in the open reading frame sequence of Candida albicans CaTOR1 in C. albicans genomic database (www.candidagenome.org). We therefore cloned and sequenced the DNA regions up- and down-stream of the interruption sites. The heterozygous mutant, but not the homozygous mutant, deleted for CaTOR1 were successfully obtained by the URA-blaster cassette method and verified by PCR method. The heterozygous mutant of CaTOR1 renders Candida cells sensitive to rapamycin, but not to Li+, Na+, K+ or Ca2+ ions. In addition, the heterozygous mutant is not sensitive to calcofluor white and Congo red and has no effect on the morphological development in C. albicans.In Saccharomyces cerevisiae,ScTCO89 encodes one of TORC1 components. Previous studies show that deletion of ScTCO89 causes cells hypersensitive to rapamycin and decreased cellular integrity. Here, we provide evidence showing that deletion of ScTCO89 causes yeast cells hypersensitive to salt stress in a high osmolarity glycerol pathway-independent fashion. In addition, we found that deletion of genes ScPTC1 or ScPTC6, encoding type 2C protein phosphatases, caused yeast cells sensitive to rapamycin. Overexpression of ScPTC6 in the high-copy plasmid pRS426 caused yeast cells greater rapamycin resistance. Taken together, these results indicate that ScPTC6 confers a rapamycin resistant function in yeast cells.