The A alpha mating locus of Schizophyllum commune encodes two dissimilar multiallelic homeodomain proteins.

The A alpha mating locus is one of four multiallelic loci that govern sexual development in the basidiomycete fungus Schizophyllum commune. We have determined the nucleotide sequence encoding three A alpha mating types, A alpha 1, A alpha 3, and A alpha 4. We have found that the locus for A alpha 3 and A alpha 4 consists of two genes: Y and Z. The locus for A alpha 1 encodes only one gene, Y. The Z polypeptides encoded by different alleles exhibit 42% identity. The Y polypeptides exhibit 49-54% identity. The finding that the deduced Z and Y polypeptides have homeodomain motifs suggests that these polypeptides may be DNA-binding regulatory proteins that control the expression of developmental genes. The deduced Z polypeptide also has acidic regions that might be functionally analogous to the acidic regions in yeast GAL4 and GCN4 that activate transcription. The Y polypeptide has a serine-rich region and a basic region that shows some identity to the lysine-rich region of H1 histones.