MOLECULAR CHARACTERIZATION OF MATING-TYPE LOCI IN SELECTED HOMOTHALLIC SPECIES OF NEUROSPORA, GELASINOSPORA AND ANIXIELLA

The mating-type loci of selected homothallic members of the Sordariaceae have been compared with the mating-type locus of the heterothallic Neurospora crassa. The N. crassa A mating-type idiomorph is present in its entirety in all homothallic strains tested with the exception of N. terricola, which is missing approximately 1.0 kbp. In N. crassa, this 1.0 kbp region contains an open reading frame for a polypeptide with a DNA-binding domain. Earlier mutational analyses show that this region is involved in events following fertilization Some 700 bp of the N. crassa a idiomorph are also absent from the genomes of all homothallic strains tested. A I I kbp region to the immediate left of the N. crassa mating-type locus is present in the genomes of all the homothallic species and is contiguous with the a idiomorph in most isolates. At least 2 kbp from the right flank of the N. crassa mating-type locus is not present in any of the homothallic strains tested. The absence of regions in and around the mating-type locus is discussed in light of the molecular function of the N. crassa mating-type region.