ISOLATION OF THE MESSENGER-RNA-CAPPING ENZYME AND FERRIC-REDUCTASE-RELATED GENES FROM CANDIDA-ALBICANS

The mRNA-capping enzyme (mRNA 5'-guanylyltransferase) gene was cloned from a Candida albicans genomic DNA library by functional complementat ion of a Saccharomyces cerevisiae ceg1 Delta null mutation. This gene, referred to as CGT1 (C. albicans guanylyltransferase 1), can encode a 52 kDa protein that is highly homologous to S. cerevisiae Ceg1p. CGT1 in a single-copy plasmid complemented the lethality of the S. cerevis iae ceg1 Delta null mutation and, like 5. cerevisiae Ceg1p, bacteriall y expressed Cgt1p was able to form a stable complex with the GMP moiet y of GTP and to synthesize the cap structure in vitro, demonstrating t hat CGT1 is the C. albicans mRNA 5'-guanylyltransferase gene. CGT1 see med to exist as a single copy in the C. albicans genome and was active ly transcribed into mRNA. Another ORF was found in an opposite strand very close to the CGT1 locus. This gene shared significant sequence ho mology with S. cerevisiae FRE1, the gene encoding ferric reductase, an d therefore was designated CFL1 (C. albicans ferric-reductase-like gen e 1). Despite its sequence homology with 5. cerevisiae FRE1, CFL1 mRMA was not induced by iron deprivation, and CFL1 did not complement the slow growth of a S. cerevisiae fre1 Delta null mutant in the absence o f iron, suggesting that CFL1 is functionally distinct from S. cerevisi ae FRE1.