Studies on a Suppressor of Non-Allelic Acetate-Requiring Mutants of Neurospora

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Abstract
Three acetate-requiring strains, S-34, S-210, and S-48 each differed from wild type by a single gene mutation. Crosses between combinations of 2 mutants gave segregation for wild type in ascus dissections, indicating non-allelism of the 3 mutants. Control inoculations of each member of a pair on minimal medium checked for back mutations. A double mutant having 2 mutant loci was demonstrated by segregations from a cross between a segregate from (S-48a X S-210a) X S-48a, and wild type. A culture from S-34 which grew to a limited extent on minimal medium was crossed with wild type. In each of 4 resulting asci which had complete germination of ascospores, there was segregation for"leaky" spores which gave approx. 1/4 the normal growth. The"leaky" phenomenon was due to a suppressor gene at a locus other than that for acetate requirement. The suppressor was not specific for S-34 as shown by crosses with S-210 and S-48. On the assumption that the suppressor gene permitted limited acetate synthesis from a carbon source such as glycerol by removing the inhbition caused by a product of glucose metabolism, the mutants with and without the suppressor were grown on media containing glucose or glycerol, both with and without a supplement of acetate. Mutants with the suppressor gene grew to a certain extent on unsupplemented medium with glucose as a carbon source, indicating that the suppressor had partially removed the inhibition. When glycerol was used as a carbon source the mutant with the suppressor did not show any increased weight over that of the mutant without the suppressor gene. This suggested that the suppressor operated through the same pathway of acetate production as when glycerol was the carbon source, producing limited amts. of acetate, since supplementing the medium with acetate markedly increased growth.

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