Purine-excreting mutants ofSaccharomyces cerevisiae: I. Isolation and genetic analysis

Abstract

SUMMARYPurine-excreting mutants of yeast have been obtained by selecting for (a) adenine-insensitive pigment accumulation in a strain carryingad-2and (b) by isolating prototrophic mutants which crossfeed to an adenine-requiring indicator strain. The first method yielded both auxotrophic and prototrophic mutants. The auxotrophs were assigned toad-12which specifies adenylosuccinate synthetase. The prototrophs were affected by a gene,su-pur, which prevented purine excretion, and the majority of them showed anomalous behaviour of mating-typeaassociated with the mutations causing excretion. Mutants obtained by the second method were allocated to six unlinked genes. Those assigned topur-1topur-5are recessive and affected bysu-pur. pur-6is a complex locus with both dominant and recessive alleles; it is closely linked or allelic tosu-purandad-4. Functional tests involving mutants ofpur-3andpur-6in combination withpur-1andpur-4did not show normal intergenic complementation. The suppressor shows gene-specific dominance/recessiveness. Some metabolic lesions which could give rise to purine excretion are discussed.