Mutations Affecting the Repressibility of Arginine Biosynthetic Enzymes in Sacchromyces cerevisiae

Abstract

A method is described for isolating mutants of Saccharomyces cerevisiae which have lost repressibility by exogenous arginine for ornithine transcarbamylase. Besides permeability mutants, three complementary classes of mutations were found: argRI, argRII and argRIII which are recessive and define three loci. No evidence for a linkage between any of these three loci or with the gene coding for ornithine transcarbamylase has been obtained. Strains bearing mutations at either of these loci cannot be distinguished on a phenotype basis: after growth on minimal medium, the l‐ornithine carbamoyl transferase activity is twice that of the wild type strain; the mutations modify neither the growth rate nor the permeability to arginine. The mutations might affect the structure of an hetero‐polypeptidic aporepressor. The level of ornithine transcarbamylase in diploids is proportional to the number of argF+ genes in regulated as well as in non‐regulated cells. Copyright © 1970, Wiley Blackwell. All rights reserved