Vegetative Incompatibility in the het-6 Region of Neurospora crassa Is Mediated by Two Linked Genes

Corresponding author: M. L. Smith, Biology Department, Carleton University, 1125 Colonel By Dr., Ottawa, Ontario K1S 5B6, Canada., mysmith{at}ccs.carleton.ca (E-mail)

Communicating editor: R. H. DAVIS

Non-self-recognition during asexual growth of Neurospora crassa involves restriction of heterokaryon formation via genetic differences at 11 het loci, including mating type. The het-6 locus maps to a 250-kbp region of LGIIL. We used restriction fragment length polymorphisms in progeny with crossovers in the het-6 region and a DNA transformation assay to identify two genes in a 25-kbp region that have vegetative incompatibility activity. The predicted product of one of these genes, which we designate het-6^OR, has three regions of amino acid sequence similarity to the predicted product of the het-e vegetative incompatibility gene in Podospora anserina and to the predicted product of tol, which mediates mating-type vegetative incompatibility in N. crassa. The predicted product of the alternative het-6 allele, HET-6^PA, shares only 68% amino acid identity with HET-6^OR. The second incompatibility gene, un-24^OR, encodes the large subunit of ribonucleotide reductase, which is essential for de novo synthesis of DNA. A region in the carboxyl-terminal portion of UN-24 is associated with incompatibility and is variable between un-24^OR and the alternative allele un-24^PA. Linkage analysis indicates that the 25-kbp un-24-het-6 region is inherited as a block, suggesting that a nonallelic interaction may occur between un-24 and het-6 and possibly other loci within this region to mediate vegetative incompatibility in the het-6 region of N. crassa.

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