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

Abstract

Purine-excreting mutants of yeast have been obtained by selecting for (a) adenine-insensitive pigment accumulation in a strain carrying ad-2 and (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 to ad-12 which 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-type a associated with the mutations causing excretion. Mutants obtained by the second method were allocated to six unlinked genes. Those assigned to pur-1 to pur-5 are recessive and affected by su-pur. pur-6 is a complex locus with both dominant and recessive alleles; it is closely linked or allelic to su-pur and ad-4. Functional tests involving mutants of pur-3 and pur-6 in combination with pur-1 and pur-4 did not show normal intergenic complementation. The suppressor shows gene-specific dominance/recessiveness. Some metabolic lesions which could give rise to purine excretion are discussed.