A Dominance Modifier for Cycloheximide Resistance in Coprinus cinereus

SUMMARY: Wild and laboratory strains of Coprinus cinereus show varying levels of sensitivity to cycloheximide (actidione). Mutants resistant to 1.0 μg cycloheximide ml-1 were isolated from UV light-irradiated oidia of two strains unable to grow on more than 0.25 μg cycloheximide ml-1. Of 13 induced mutants, 12 fell into one complementation group, cy-2; mutants at this locus were usually recessive, but one of those isolated carried a dominance modifier gene, modcy +, which led to partial resistance in dikaryons heterozygous for cy-2 r. Modcy+ was dominant in dikaryons to its non-mutant allele modcy -, but it had no effect in diploids. However, it affected all cy-2 r alleles tested in dikaryons. Linkage data are presented for cy-2, modcy and another cycloheximide resistance gene, cy-1, which is found in wild strains.