title: A nonself recognition gene complex in Neurospora crassa.
abstract: Nonself recognition is exemplified in the fungal kingdom by the regulation of cell fusion events between genetically different individuals (heterokaryosis). The het-6 locus is one of approximately 10 loci that control heterokaryon incompatibility during vegetative growth of N. crassa. Previously, it was found that het-6-associated incompatibility in Oak Ridge (OR) strains involves two contiguous genes, het-6 and un-24. The OR allele of either gene causes "strong" incompatibility (cell death) when transformed into Panama (PA)-background strains. Several remarkable features of the locus include the nature of these incompatibility genes (het-6 is a member of a repetitive gene family and un-24 also encodes the large subunit of ribonucleotide reductase) and the observation that un-24 and het-6 are in severe linkage disequilibrium. Here, we identify "weak" (slow, aberrant growth) incompatibility activities by un-24PA and het-6PA when transformed separately into OR strains, whereas together they exhibit an additive, strong effect. We synthesized strains with the new allelic combinations un-24PA het-6OR and un-24OR het-6PA, which are not found in nature. These strains grow normally and have distinct nonself recognition capabilities but may have reduced fitness. Comparing the Oak Ridge and Panama het-6 regions revealed a paracentric inversion, the architecture of which provides insights into the evolution of the un-24-het-6 gene complex.
authors.affiliation: Biology Department, Carleton University, Ottawa, Ontario K1S 5B6, Canada.
authors.forename: Cristina O
authors.initials: CO
authors.lastname: Micali
authors.forename: Myron L
authors.initials: ML
authors.lastname: Smith
mesh_terms: D007446:Chromosome Inversion; D003227:Conjugation, Genetic / Q000235:genetics*; D019143:Evolution, Molecular; D005656:Fungal Proteins / Q000235:genetics* / Q000378:metabolism; D005800:Genes, Fungal / Q000235:genetics*; D015810:Linkage Disequilibrium; D009492:Neurospora crassa / Q000235:genetics* / Q000254:growth & development
chemical_list: D005656:Fungal Proteins