Cloning and characterization of a Schizophyllum gene with A beta 6 mating-type activity.

The A-pathway of development in the basidiomycete fungus Schizophyllum commune may be activated by either of two mating-type loci, A alpha and A beta. A alpha consists of two multiallelic genes, Y and Z. Y contains a putative homeodomain; Z contains a homeodomain-related region. Non-self combinations of Y and Z form heteromultimers which are thought to be transcription factors of developmental genes. To more completely understand A-regulated development it is necessary to address the issue of functional redundancy, i.e., how do two different mating loci, A alpha and A beta, both manage to regulate the same pathway. Here we report the structure of a gene with A beta 6 activity. This gene, denoted A beta V6, encodes a deduced polypeptide of 640 amino-acids with a homeodomain motif. V6 also contains a 20-amino acid sequence that is conserved in A alpha Y1, Y3 and Y4. Except for the homeodomain and the conserved sequence, the deduced V6 polypeptide shows no significant identity to A alpha Y, A alpha Z, or other known proteins. The presence of a homeodomain suggests that V, like Y and Z, may be a regulatory protein for genes in the A-pathway. Thus while A alpha and A beta encode different proteins, the general mechanism by which A alpha and A beta components signal A-regulated development may be similar.