pfam07217 Het-C Heterokaryon incompatibility protein Het-C. In filamentous fungi het loci (for heterokaryon incompatibility) are believed to regulate self/nonself-recognition during vegetative growth. As filamentous fungi grow hyphal fusion occurs within an individual colony to form a network. Hyphal fusion can occur also between different individuals to form a heterokaryon in which genetically distinct nuclei occupy a common cytoplasm. However heterokaryotic cells are viable only if the individuals involved have identical alleles at all het loci.