Cloning and comparison of Aα mating-type alleles of the basidiomycete Schizophyllum commune

Summary

An Aα mating-type allele (Aα4) was isolated by walking the chromosome from the closely linked PAB1 gene. A cosmid clone containing the Aα1 allele isolated from the walk was used as a probe to recover the Aα1 allele from another cosmid library. Cosmids encoding mating-type activity were identified by transforming Schizophyllum cells and screening for activation of A-regulated development. Putative mating-type transformants were confirmed in mating tests and genetic analyses of progeny. The identity of the specific alleles isolated was demonstrated by showing that their effectiveness in transforming for mating type is limited to recipient strains possessing an Aα allele different from the one encoded by the cloned sequences. Transforming DNA is active in trans, suggesting that Aα encodes a diffusible product. Restriction mapping shows that Aα1 and Aα4 are coded in the same physical region of the genome, but within a subregion that contains extensive sequence divergence. In addition, Southern analyses show that there is only one copy of Aα1 or Aα4 per haploid genome, and that they do not cross-hybridize to one another or to any of the other Aα alleles. Aα1 and Aα4 were subcloned as 2.8 and 1.2 kb fragments, respectively, retaining in transformation all the mating-type activity demonstrated of the original cosmids.