The A alpha mating-type locus of Schizophyllum commune: structure and function of gene X.

Gene X maps immediately right of gene Y at the A alpha mating-type locus in Schizophyllum commune. Alleles X1, X3 and X4 were isolated, subcloned, and sequenced. The structure of the alleles and their relationship to the A alpha locus is described. The deduced X isoforms possess no recognized motifs common to other polypeptides and no significant similarity to any sequences in the protein data-bases. X alleles do not activate A-regulated development when transformed into recipient strains possessing different A alpha mating types or when these transformants are mated with tester strains. An X1-disrupted construction yielded a high frequency (33%) of homologous gene replacements. X-disrupted mutants have wild-type phenotypes and mate normally. Both the functional analyses and sequence data for X1, X3, and X4 suggest that the right boundary of the A alpha mating-type locus falls between A alpha Y and X. We propose that the Z and Y genes constitute the A alpha locus in its entirety.