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Abstract:
Fungal pheromones have been demonstrated to function in the initial recognition of the fungal mating process. One type of peptide pheromones, identified in the Ascomycetes and Basidiomycetes, terminate in a conserved CAAX motif which triggers sequential post-translational modifications of the pheromone precursors. Among this type of peptide pheromones, a well-studied one is the a-factor of Saccharomyces cerevisiae. The mature a-factor is exported from the cell via an alternative mechanism involving the ATP-binding cassette transporter Ste6p, which is distinct from the typical secretory pathway utilized by most peptides. Unlike the Ascomycetes, the basidiomyceteous fungi produce only CAAX motif containing lipopeptide pheromones. Cryptococcus neoformans, a human pathogenic basidiomycetous yeast, causes the life-threatening meningoencephalitis mainly in individuals with compromised immune functions. Virulence studies of the congenic pair of C. neoformans strains have shown that MATalpha cells are more virulent thanMATa cells. Characterization of mating pheromone genes in the MATalpha strains have suggested an autocrine signaling loop may function and contribute to the virulence of the MATalpha cells. To further address the role of pheromone in the signaling loop, we have identified STE6 homologue in the C. neoformans genome project at SGTC and begun to dissect its function. By disrupting theSTE6, we found that ste6 mutants in either MATalpha orMATa background showed partially impaired mating function, although slight differences were noticed. However, when ste6 MATalpha andMATa mutants cross with each other, the mating process was nearly completely abolished. Our data indicates that the STE6 functions bilaterally and is required but not essential for mating in C. neoformans.
