Resistance to p-fluorophenylalanine in diploid/haploid dikaryons: dominance modifier gene explained as a controller of hybrid multimer formation

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Abstract
SUMMARY: The gene pfpr-10 in Coprinus confers resistance to p-fluorophenylalanine. The resistance of the heterozygote pfpr-10/pfp8-10 is completely recessive, both in diploids and dikaryons. A dominance modifier Mod+ makes pfpr-10 dominant in a dikaryon but not in a cliploid. It also enhances the degree of resistance in r homozygotes. These results are explained on a hypothetical model based upon a hexameric product of the pfpr-10 gene, with resistance to PFP being proportional to the percentage of homo r hexamers. The Mod+ is presumed to act by keeping the r and s products separate so that hybrid multimers are reduced to a minimum. Critical threshold concentrations of PFP for diploid/haploid dikaryons in 40 different combinations of pfpr and Mod+ genes cover a wide range of gene doses and percentage of homo r multimers. The relationship between the critical threshold concentrations and the calculated percentage of homo r multimers supports the model.