Proteome's fungal databases, YPD (for Saccharomyces cerevisiae), PombePD (for Schizosaccharomyces pombe), and CalPD (for Candida albicans), work together to present a comprehensive view of the molecular and cell biology of the genes and proteins of the fungal world. YPD, CalPD, and PombePD are part of a group of databases collectively called the BioKnowledge Library, which also includes databases for complex organisms, such as the worm Caenorhabditis elegans (WormPD), a model for development of a multicellular organism, and a protein survey database for humans. This chapter we provide detailed coverage of the YPD database, which has served as the prototype for the creation of all other volumes of the BioKnowledge Library. The chapter presents the unique features of the newer fungal databases PombePD and CalPD. CalPD is expected to be incorporated into MycoPathPD, a new volume that will include genes and proteins of C. albicans and other human pathogenic fungi. YPD is recommended as a good initiation site for newcomers.

The ability to undergo morphological change has been reported as an advantageous trait in fungal pathogenesis. Here we demonstrate that Candida glabrata ATCC2001, like diploid Saccharomyces cerevisiae strains, forms elongated chains of pseudohyphal cells on solid nitrogen starvation media (SLAD). Constrictions were apparent between adjoining cells; no parallel-sided hyphae were seen and pseudohyphae invaded the agar. When SLAD was supplemented with ammonium sulfate both C. glabrata and diploid S. cerevisiae strains lost their ability to undergo pseudohyphal growth. However, on this media C. glabrata yeast cells invaded the agar in a similar fashion to the invasive growth mode exhibited by haploid strains of S. cerevisiae cultured on rich media such as YPD. C. glabrata was not capable of invading YPD demonstrating that the process of filamentation is distinct in these two fungi. To our knowledge this is the first report to demonstrate that C. glabrata can undergo morphological change and grow as an invasive filamentous organism.

ABSTRACT Cpp1p is a putative mitogen-activated protein (MAP) kinase phosphatase that suppresses Candida albicans hyphal formation at 25°C through its probable substrate, the Cek1p filamentation MAP kinase. Here we report that expression of the serum-induced genes SAP4-6 and HYR1 increased several fold in hyphal forms of a cpp1/cpp1 null mutant, while the rate and extent of hyphal development up to 5 h were normal. Therefore, we provide evidence that Cpp1p represses hyphal gene expression by acting through a Cek1p-independent mechanism. SAP4-6 and HYR1 transcripts were undetectable in a null mutant of another key regulator of filamentation, Efg1p; thus, Efg1p and Cpp1p oppose each other during the expression of these genes in hyphal forms.

ABSTRACT Extracellular signal-regulated protein kinase (ERK, or mitogen-activated protein kinase [MAPK]) regulatory cascades in fungi turn on transcription factors that control developmental processes, stress responses, and cell wall integrity. CEK1 encodes a Candida albicans MAPK homolog (Cek1p), isolated by its ability to interfere with the Saccharomyces cerevisiae MAPK mating pathway. C. albicans cells with a deletion of the CEK1 gene are defective in shifting from a unicellular budding colonial growth mode to an agar-invasive hyphal growth mode when nutrients become limiting on solid medium with mannitol as a carbon source or on glucose when nitrogen is severely limited. The same phenotype is seen in C. albicans mutants in which the homologs ( CST20 , HST7 , and CPH1 ) of the S. cerevisiae STE20 , STE7 , and STE12 genes are disrupted. In S. cerevisiae , the products of these genes function as part of a MAPK cascade required for mating and invasiveness of haploid cells and for pseudohyphal development of diploid cells. Epistasis studies revealed that the C. albicans CST20 , HST7 , CEK1 , and CPH1 gene products lie in an equivalent, canonical, MAPK cascade. While Cek1p acts as part of the MAPK cascade involved in starvation-specific hyphal development, it may also play independent roles in C. albicans . In contrast to disruptions of the HST7 and CPH1 genes, disruption of the CEK1 gene adversely affects the growth of serum-induced mycelial colonies and attenuates virulence in a mouse model for systemic candidiasis.

Candida albicans strains with a deletion of the mitogen‐activated protein kinase tyrosine phosphatase gene (CPP1) are derepressed in the yeast‐to‐hyphal transition on solid surfaces in vitro at ambient temperatures and this gene is therefore required for repression of the yeast‐to‐hyphal switch. The pathology caused by a CPP1 null mutant strain was compared with that of the null mutant into which the wild‐type CPP1 gene was introduced by homologous recombination and with the wild‐type parent strain in a murine mycotic mastitis model. The mammary glands of lactating mice (at day 5 postpartum) were infected for 2, 4 and 6 days with 1 times 105, 1 times 106 and 1 times 107 cell‐forming units before euthanasia. Infected and non‐infected control glands were evaluated histopathologically. The null mutant strains showed less severe pathology than the two control strains. The Cpp1p tyrosine phosphatase may thus be considered a virulence determinant during localized infection in C. albicans.

Candida albicans strains with a deletion of the mitogen-activated protein kinase CEK1 gene are defective in the yeast to hyphal transition on solid surfaces in vitro. The virulence of a cek1 delta/cek1 delta null mutant strain was compared with its wild-type parent strain (WT) in a novel model of localized candidiasis. The mammary glands of lactating mice (at day 5 postpartum) were infected for 2, 4 and 6 days with 50 microliter suspension containing 1 x 10(5), 1 x 10(6) and 1 x 10(7) blastopores before death. Infected and non-infected control glands were evaluated pathologically. All animals infected with cek1 delta/cek1 delta null mutant strains showed no lesions while 65% of animals infected with the WT strain had severe lesions characterized by widespread heterophilic infiltration, necrosis, and abscess formation. As an additional control, animals infected with the disrupted strain complemented with the WT CEK1, on a replicating plasmid, also showed severe pathological changes similar to the WT strain. These results clearly demonstrate that the CEK1 gene codes for a virulence determinant of C. albicans and that the mouse mastitis model is well suited for the discriminative study of the pathogenicity of different C. albicans strains.

Mitogen-activated protein (MAP) kinases are pivotal components of eukaryotic signaling cascades. Phosphorylation of tyrosine and threonine residues activates MAP kinases, but either dual-specificity or monospecificity phosphatases can inactivate them. The Candida albicans CPP1 gene, a structural member of the VH1 family of dual-specificity phosphatases, was previously cloned by its ability to block the pheromone response MAP kinase cascade in Saccharomyces cerevisiae. Cpp1p inactivated mammalian MAP kinases in vitro and acted as a tyrosine-specific enzyme. In C. albicans a MAP kinase cascade can trigger the transition from the budding yeast form to a more invasive filamentous form. Disruption of the CPP1 gene in C. albicans derepressed the yeast to hyphal transition at ambient temperatures, on solid surfaces. A hyphal growth rate defect under physiological conditions in vitro was also observed and could explain a reduction in virulence associated with reduced fungal burden in the kidneys seen in a systemic mouse model. A hyper-hyphal pathway may thus have some detrimental effects on C. albicans cells. Disruption of the MAP kinase homologue CEK1 suppressed the morphological effects of the CPP1 disruption in C. albicans. The results presented here demonstrate the biological importance of a tyrosine phosphatase in cell-fate decisions and virulence in C. albicans.

We have determined the nucleotide sequence of a protozoan aminoacyl-tRNA synthetase. The isoleucyl-tRNA synthetase (ileRS) gene [ilsA; formerly cupC, Martindale, D. W., Martindale, H. M., and Bruns, P. J. (1986) Nucleic Acids Res. 14, 1341-1354] from the ciliate Tetrahymena thermophila was sequenced and found to have eight introns, four transcription start sites, and a putative polypeptide of 1081 amino acids. A polypeptide 20 amino acids longer could be made if a transcribed in-frame ATG close to the start sites and with suboptimal sequence context is used. This gene was identified through hybridization and amino acid sequence similarity to the previously cloned and sequenced ileRS (cytoplasmic) gene from Saccharomyces cerevisiae [Englisch, U., Englisch, S., Markmeyer, P., Schischkoff, J., Sternbach, H., Kratzin, H., and Cramer, F. (1987) Biol. Chem. Hoppe-Seyler 368, 971-979; Martindale, D. W., Gu, Z. M., and Csank, C. (1989) Curr. Genet. 15, 99-106] with which it shares 47% of its amino acids. We also compared it to ileRS genes from E. coli and an archaebacterium. Two leucine zippers motifs were identified in the carboxyl-terminal domain of the polypeptide; one of these motifs is in the same area as the zinc finger motif found in the E. coli enzyme. The transcription pattern of the ilsA gene was monitored under various culture conditions and parallels changes in protein synthesis.