The pathogenic yeast Candida albicans regulates its cellular morphology in response to environmental conditions. Ellipsoidal, single cells (blastospores) predominate in rich media, whereas filaments composed of elongated cells that are attached end-to-end form in response to starvation, serum, and other conditions. The TUP1 gene, which encodes a general transcriptional repressor in Saccharomyces cerevisiae, was isolated from C. albicans and disrupted. The resulting tup1 mutant strain of C. albicans grew exclusively as filaments under all conditions tested. TUP1 was epistatic to the transcriptional activator CPH1, previously found to promote filamentous growth. The results suggest a model where TUP1 represses genes responsible for initiating filamentous growth and this repression is lifted under inducing environmental conditions.

No abstract

contributed equally to this workIn response to a variety of external signals, the fungal pathogen Candida albicans undergoes a transition between ellipsoidal single cells (blastospores) and ®la-ments composed of elongated cells attached end-toend. Here we identify a DNA-binding protein, Nrg1, that represses ®lamentous growth in Candida probably by acting through the co-repressor Tup1. nrg1 mutant cells are predominantly ®lamentous under non-®lament-inducing conditions and their colony morphology resembles that of tup1 mutants. We also identify two ®lament-speci®c genes, ECE1 and HWP1, whose transcription is repressed by Nrg1 under noninducing conditions. These genes constitute a subset of those under Tup1 control, providing further evidence that Nrg1 acts by recruiting Tup1 to target genes. We show that growth in serum at 37°C, a potent inducer of ®lamentous growth, causes a reduction of NRG1 mRNA, suggesting that ®lamentous growth is induced by the down-regulation of NRG1. Consistent with this idea, expression of NRG1 from a non-regulated promoter partially blocks the induction of ®lamentous growth.

Recent sequencing and assembly of the genome for the fungal pathogen Candida albicans used simple automated procedures for the identification of putative genes. We have reviewed the entire assembly, both by hand and with additional bioinformatic resources, to accurately map and describe 6,354 genes and to identify 246 genes whose original database entries contained sequencing errors (or possibly mutations) that affect their reading frame. Comparison with other fungal genomes permitted the identification of numerous fungus-specific genes that might be targeted for antifungal therapy. We also observed that, compared to other fungi, the protein-coding sequences in the C. albicans genome are especially rich in short sequence repeats. Finally, our improved annotation permitted a detailed analysis of several multigene families, and comparative genomic studies showed that C. albicans has a far greater catabolic range, encoding respiratory Complex 1, several novel oxidoreductases and ketone body degrading enzymes, malonyl-CoA and enoyl-CoA carriers, several novel amino acid degrading enzymes, a variety of secreted catabolic lipases and proteases, and numerous transporters to assimilate the resulting nutrients. The results of these efforts will ensure that the Candida research community has uniform and comprehensive genomic information for medical research as well as for future diagnostic and therapeutic applications.

A photocrosslinking nucleotide, 5‐[N‐(p‐azidobenzoyl)‐3‐aminoallyl]‐deoxyuridine monophosphate (N3Rd‐UMP), has been used to identify four polypeptides that are associated with the large Saccharomyces cerevisiae RNA polymerase III transcription factor TFIIIC, and to map the locations of these subunits along DNA when TFIIIC binds to the S.cerevisiae SUP4 tRNA(Tyr) gene. The 145 kd subunit of TFIIIC is primarily accessible to photocrosslinking from the vicinity of the box B + internal promoter element; 95 and 55 kd subunits are located on opposite sides of the DNA helix in the vicinity of the box A internal promoter element; a 135 kd subunit is less strongly crosslinked to the box A region and to a DNA segment between boxes B and A. DNA probes containing more than one N3RdUMP residue can form crosslinks between polypeptide chains. The specific circumstances of formation and the apparent mol. wts of two of these products lead to the tentative suggestion that a protomer of TFIIIC may contain two 95 kd subunits.