MFalpha1, the gene encoding the alpha mating pheromone of Candida albicans

Candida albicans, the single most frequently isolated human fungal pathogen, was thought to be asexual until the recent discovery of the mating-type-like locus (MTL). Homozygous MTL strains were constructed and shown to mate. Furthermore, it has been demonstrated that opaque-phase cells are more efficient in mating than white-phase cells. The similarity of the genes involved in the mating pathway in Saccharomyces cerevisiae and C. albicans includes at least one gene (KEX2) that is involved in the processing of the α mating pheromone in the two yeasts. Taking into account this similarity, we searched the C. albicans genome for sequences that would encode the α pheromone gene. Here we report the isolation and characterization of the gene MFα1, which codes for the precursor of the α mating pheromone in C. albicans. Two active α-peptides, 13 and 14 amino acids long, would be generated after the precursor molecule is processed in C. albicans. To examine the role of this gene in mating, we constructed an mfα1 null mutant of C. albicans. The mfα1 null mutant fails to mate as MTLα, while MTLa mfα1 cells are still mating competent. Experiments performed with the synthetic α-peptides show that they are capable of inducing growth arrest, as demonstrated by halo tests, and also induce shmooing in MTLa cells of C. albicans. These peptides are also able to complement the mating defect of an MTLα kex2 mutant strain when added exogenously, thereby confirming their roles as α mating pheromones.     

Mutations in a gene encoding the alpha subunit of a Saccharomyces cerevisiae G protein indicate a role in mating pheromone signaling.

Mutations which allowed conjugation by Saccharomyces cerevisiae cells lacking a mating pheromone receptor gene were selected. One of the genes defined by such mutations was isolated from a yeast genomic library by complementation of a temperature-sensitive mutation and is identical to the gene GPA1 (also known as SCG1), recently shown to be highly homologous to genes encoding the alpha subunits of mammalian G proteins. Physiological analysis of temperature-sensitive gpa1 mutations suggests that the encoded G protein is involved in signaling in response to mating pheromones. Mutational disruption of G-protein activity causes cell-cycle arrest in G1, deposition of mating-specific cell surface agglutinins, and induction of pheromone-specific mRNAs, all of which are responses to pheromone in wild-type cells. In addition, mutants can conjugate without the benefit of mating pheromone or pheromone receptor. A model is presented where the activated G protein has a negative impact on a constitutive signal which normally keeps the pheromone response repressed.     

Nucleotide sequence of the RAD10 gene of Saccharomyces cerevisiae.

The RAD10 gene is one of several genes in Saccharomyces cerevisiae required for incision of u.v.-irradiated or cross-linked DNA. We have determined the nucleotide sequence of the RAD10 gene and its flanking regions. The RAD10 nucleotide sequence presented here differs significantly from that recently reported. The RAD10 protein predicted from the nucleotide sequence contains 210 amino acids with a calculated mol. wt. of 24 310. The middle portion of the RAD10 protein, which is highly basic and also contains eight of the total of 10 tyrosine residues present in the protein, may be involved in DNA binding by ionic interactions and tyrosine intercalation between the bases of DNA. A genomic deletion of the entire RAD10 gene does not affect viability; however, the rad10 deletion mutant is highly u.v. sensitive.