The Cryptococcus neoformans STE12alpha gene: a putative Saccharomyces cerevisiae STE12 homologue that is mating type specific.

Cryptococcus neoformans possesses two mating types, MATalpha and MATa. Alpha-Cells are more virulent than a-cells and are also, unlike a-cells, capable of producing extensive hyphae in the haploid phase. The molecular analysis of hyphae production in C. neoformans has resulted in the identification of a gene which displays substantial similarity to other fungal STE12 genes, including the presence of a highly conserved homeodomain. Overexpression of the C. neoformans gene resulted in poor growth, altered morphology and the presence of hyphal projections, phenotypes reported in similar studies of the Saccharomyces cerevisiae STE12 gene. Overexpression was also found to induce MFalpha, a pheromone, and CNLAC1, a confirmed C. neoformans virulence gene. The C. neoformans STE12alpha gene, however, has one striking difference from other fungal STE12 genes; it is found only in alpha-cells. The existence of STE12alpha in C. neoformans suggests that this fungus has elements of a conserved MAP kinase cascade, which may be organized in a novel manner.