Suppression of acetate mutants in Coprinus : II. Correlation of recessiveness and dosage effects with suppressed enzyme level.

Recessiveness and dosage effects of two suppressor genes in Coprinus were correlated with suppressed enzyme activity in cell free extracts. Wild type, the suppressible acu-1.4 mutation and suppressor gene mutations supa4.1(+) and supa4.2(+) were used to construct appropriate diploid strains which allowed comparison of the following situations: (i) wild type, (ii) unsuppressed mutant (iii) homoallelism for a single suppressor, (iv) heterozygosity for a single suppressor (sup (+)/sup (-)) and (v)heterozygosity for two nonallelic suppressors. Extracts of the unsuppressed mutant had no enzyme activity whereas extracts of both the homoallelic suppressor strains had the suppressed level of some 20% wild type acetyl-CoA synthetase activity. Diploids heterozygous for sup (+)/sup (-) were acu(-) in phenotype. These had only 3-6% wild type enzyme activity, a level too low to support growth on acetate and hence the apparent recessiveness of each sup (+) mutation. The doubly heterozygous diploid had exactly the same level of enzyme activity as homoallelic diploids, 20% wild type, hence the acu (+) suppressed phenotype.