Mutations Affecting the Repressibility of Arginine Biosynthetic Enzymes in Sacchromyces cerevisiae



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.


l-Ornithine transcarbamylase (EC


phospho-N-acetyl glutamate, NADPH2 oxidoreductase, or phospho-N-acetyl glutamate dehydrogenase


ATP: N-acetyl glutamate phosphotransferase, or N-acetyl glutamate kinase