Isolation and genetic characterization of a mutation affecting ribosomal resistance to cycloheximide in Tetrahymena

A dominant mutation at a new locus affecting resistance to cycloheximide has been isolated by exploiting a synergistic relationship with a previously known mutation for cycloheximide resistance in Tetrahymena. The new mutation (ChxB) was induced in a line homozygous for ChxA and was recovered from that background by a new technique termed interrupted genomic exclusion. Segregation data from the interrupted genomic exclusion suggest that ChxA and ChxB are separate, linked loci showing 30% recombination. Minimal lethal doses of cycloheximide for the four possible combinations of the wild-type and mutant alleles of these two genes are: wild type 6 microgram/ml, ChxA 125 microgram/ml, ChxB 10 microgram/ml, ChxA-ChxB 175 microgram/ml.