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 a nd A beta. A alpha consists of two multiallelic genes, Y and Z. Y cont ains a putative homeodomain; Z contains a homeodomain-related region. Non- self combinations of Y and Z form heteromultimers which are thoug ht to be transcription factors of developmental genes. To more complet ely 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 w e report the structure of a gene with A beta 6 activity. This gene, de noted A beta V6, encodes a deduced polypeptide of 640 amino-acids with a homeodomain motif. V6 also contains a 20-amino acid sequence that i s conserved in A alpha Y1, Y3 and Y4. Except for the homeodomain and t he conserved sequence, the deduced V6 polypeptide shows no significant identity to A alpha Y, A alpha Z, or other known proteins. The presen ce 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 enc ode different proteins, the general mechanism by which A alpha and A b eta components signal A-regulated development may be similar.