Deletion of the Schizophyllum commune A alpha locus: the roles of A alpha Y and Z mating-type genes.

The A alpha locus is one of four master regulatory loci that determine mating type and regulate sexual development in Schizophyllum commune. We have made a plasmid containing a URA1 gene disruption of the A alpha Y1 gene. Y1 is the sole A alpha gene in A alpha 1 strains. We used the plasmid construction to produce an A alpha null (i.e., A alpha delta) strain by replacing the genomic Y1 gene with URA1 in an A alpha 1 strain. To characterize the role of the A alpha genes in the regulation of sexual development, we transformed various A alpha Y and Z alleles into A alpha delta strains and examined the acquired mating types and mating abilities of the transformants. These experiments demonstrate that the A alpha Y gene is not essential for fungal viability and growth, that a solitary Z A alpha mating-type gene does not itself activate development, that A beta proteins are sufficient to activate the A developmental pathway in the absence of A alpha proteins and confirm that Y and Z genes are the sole determinants of A alpha mating type. The data from these experiments support and refine our model of the regulation of A-pathway events by Y and Z proteins.