Super suppressors in Neurospora crassa I. Induction, genetic localization and relationship to a missense suppressor

Abstract

Genetic analyses have been made to test the feasibility of using coincident reversions to prototrophy of multiple mutants to select super suppressors (ssu) in Neurospora crassa. Of five double-mutant strains examined, only those mutant combinations in which both members had the properties of nonsense mutations did revert coincidently. Forty-eight genetically purified coincident revertants were crossed to the wild type, and each was shown to contain a suppressor mutation. Five super suppressors were examined more thoroughly. Tetrad and random spore analysis was used to demonstrate that each behaved as a single gene in crosses. Two super suppressors, ssu-1 and ssu-4 were localized respectively on the right and left arm of linkage group 7. Two others, ssu-2 and ssu-3, appear to map on the right arm of linkage group 1. The fifth super suppressor mapped, ssu-7, lies between ad-8 and ylo-1 on linkage group 6. One super suppressor, ssu-1, was interesting because it mapped near the location reported for the suppressor of the missense mutant tryp-3(td201) (Yourno and Suskind 1964a). However, no overlap was found in action spectrum of the two suppressors. Tetrad analysis showed the two suppressors were located about 10 map units apart, the missense suppressor being the more distal to the centromere.