The product of the het-C heterokaryon incompatibility gene of Neurospora crassa has characteristics of a glycine-rich cell wall protein

Filamentous fungi are capable of hyphal fusion, but heterokaryon formation between different isolates is controlled by specific loci termed het loci. Heterokaryotic cells formed between strains of different het genotype are rapidly destroyed or strongly inhibited in their growth. In Neurospora crassa, at least 11 loci including the mating type locus, affect the capacity to form a heterokaryon between different isolates. In this report, we describe the molecular characterization of the vegetative incompatibility locus, het-C. The het-C(OR) allele was cloned by genetically identifying the het-C locus in a chromosome walk, and the activity of clones containing the het-C(OR) allele was tested in a function transformation assay. The het-C(OR) allele encodes a 966-amino acid polypeptide with a putative signal peptide; a coiled-coil motif and a C-terminal glycine-rich domain, similar to glycine-rich domains detected in various extracellular and structural cell envelope proteins. Both the coiled-coil and one-third of the glycine-rich carboxyl terminal domains were required for full het-C(OR) activity. Mutants of het-C(OR) were obtained by repeat-induced point mutation (RIP); these mutants were indistinguishable from wild type during vegetative growth and sexual reproduction but displayed dual compatibility with both mutually incompatible het-C(OR) and het-c(PA) strains.