GENETIC CONTROL OF PHOSPHORUS ASSIMILATION IN NEUROSPORA CRASSA: DOSE-DEPENDENT DOMINANCE AND RECESSIVENESS IN CONSTITUTIVE MUTANTS

Robert L. Metzenberg ¹ and William Chia ¹

¹ Department of Physiological Chemistry, University of Wisconsin, Madison, Wisconsin 53706

Mutants called nuc-1^c, constitutive for alkaline phosphatase synthesis, were isolated and mapped very close to nuc-1 mutants in which this enzyme is not expressed. nuc-1 is epistatic to nuc-1^c. nuc-1^c acts only if it is cis to normal nuc-1 function. The preparation of partial diploids heterozygous for various nuc-1 alleles is described; nuc-1^c is dominant to nuc-1⁺, which in turn is dominant to nuc-1. In heterocaryons with nuc-1⁺, nuc-1^c is dominant when it is present in high proportion, but essentially recessive if it is present in low proportions. In heterocaryons with nuc-1, nuc-1^c is again dominant when present in high proportions, but in low proportions it "complements" to give essentially normal repressibility. A model of regulation consistent with these findings is presented.