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-COR allele was cloned by genetically identifying the het-C locus in a chromosome walk, and the activity of clones containing the het-COR allele was tested in a functional transformation assay. The het-COR 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-COR activity. Mutants of het-COR 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 of two mutually incompatible het-COR and het-cPA strains.