CHARACTERIZATION OF MAT A-2, MAT A-3 AND DELTA-MATA MATING-TYPE MUTANTS OF NEUROSPORA-CRASSA

The mating-type locus of Neurospora crassa regulates mating identity a nd entry into the sexual cycle. The mar A idiomorph encodes three gene s, mat A-1, mat A-2, and mat A-3. Mutations in mat A-1 result in strai ns that have lost mating identity and vegetative incompatibility with mut a strains. A strain containing mutations in both mat A-2 and mat A -3 is able to mate, but forms few ascospores. In this study, we descri be the isolation rind characterization of a mutant deleted for mat (De lta matA), as well as mutants in either mat A-2 or mat A-3. The Delta matA strain is morphologically wild type during vegetative growth, but it is sterile and heterokaryon compatible with both mat A and mat a s trains. The mat A-2 and mat A-3 mutants are also normal during vegetat ive growth, mate as a mat A strain, and produce abundant biparental as ci in crosses with mat a, and are thus indistinguishable from a wild-t ype mat A strain. These data and the fact that the mat A-2 mat A-3 dou ble mutant makes few asci with ascospores indicate that MAT A-2 and MA T A-3 are redundant and may function in the same pathway. Analysis of the expression of two genes (sdv-1 and sdv-4) in the various mat mutan ts suggests that the mat A polypeptides function in concert to regulat e the expression of some sexual development genes.