Molecular and Functional Analyses of Incompatibility Genes at het-6 in a Population of Neurospora crassa

A Nonself Recognition Gene Complex inNeurospora crassa

“…Fitness reduction is associated with un-24 PA het-6 OR and un-24 OR het-6 PA allelic combinations: In addition to these patterns of nonsynonymous substitutions, un-24 and het-6 appear to be inherited as a block (either OR or PA) in population samples and across the species range (Mir-Rashed et al 2000;Smith et al 2000b). To explain this linkage disequilibrium, we explored the possibility that the missing allelic combinations of un-24 PA het-6 OR and un-24 OR het-6 PA may have a negative effect on fitness since vegetative incompatibility and/or sexual dysfunction have been associated with specific allelic combinations at unlinked het loci (i.e., nonallelic incompatibility) in P. anserina (Saupe 2000).…”

“…Eight of the escape strains formed vigorous heterokaryons with C8c-32 and were considered functionally un-24 OR het-6 OR whereas 7 escape strains produced spidery, selfincompatible heterokaryons and thus appeared to be functionally un-24 PA het-6 OR . All 15 escape strains were heteroallelic at un-24 on the basis of PCR analysis with primers 6JP11/6JP6 and digestion with MboI (Mir- Rashed et al 2000). Thus, the functionally PA and OR escapes were all partial diploids with silenced incompatibility activity of either the endogenous (un-24 OR ) or the ectopic (un-24 PA ) copy, respectively.…”

“…Comparison of OR and PA un-24-het-6 regions: Previously, it was suggested that linkage disequilibrium in the un-24-het-6 region may be due to sequence dissimilarity and low homologous recombination rates (Mir-Rashed et al 2000). The isolation of plB, encompassing both un-24 and het-6 PA alleles, allowed us to address this hypothesis through structural comparisons of OR and PA haplotypes.…”

“…l-Clones from the FGSC1131 library were used to study the structure of the PA haplotype. plB and pA3 (derived from FGSC1131 via FGSC2190; Smith et al 1996;Mir-Rashed et al 2000) were sequenced in the un-24 PA -het-6 PA region and used for RFLP analyses. Southern hybridizations were done to compare the marker distribution and general structure of clones carrying PA-or OR-derived sequences (Figure 1).…”

“…OR and un-24 PA het-6 PA (Mir-Rashed et al 2000;Smith et al 2000b), referred to as OR and PA haplotypes, respectively. In addition to its function in heterokaryon incompatibility, un-24 encodes the large subunit of ribonucleotide reductase, an essential enzyme that converts ribonucleotides to the deoxyribonucleotides required for DNA synthesis and repair (Smith et al 2000a).…”