Mapping the heterogeneous DNA region that determines the nine Aα mating- type specificities of Schizophyllum commune

Abstract

Classical genetic studies identified nine mating-type specificities at the Aα locus of the Basidiomycete fungus Schizophyllum commune. We have used Southern blot hybridizations to generate EcoRI restriction maps of the Aα locus for 18 strains, including all nine specificities. Aα1, Aα3 and Aα4 DNA was subcloned from three cosmids and used as probes. A unique region of DNA was found for each of the three cloned specificities. Hybridization was detected in this region only if the probe(s) and the blotted genomic DNAs were from strains with the same Aα specificity. DNAs from strains with the same Aα specificity hybridize regardless of geographic origin, but DNAs from strains with different Aα specificities do not cross-hybridize. The results demonstrate two size classes of unique Aα DNA. This unique DNA is about 4.5 kb in Aα1 strains and about 7.0-8.5 kb in other strains. Transcription regulators Z and Y, which were deduced previously from the DNA sequence of the Aα1, Aα3 and Aα4 loci, are probably encoded by all non-Aα1 loci. The smaller Aα1 loci appear to encode only Y and lack sequence for Z. No evidence was found for a locus that encodes only Z. The lack of hybridization detected between Aα loci with different specificities suggests that the evolution of Aα has resulted from extensive sequence divergence.