Use of nystatin to eliminate spontaneous revertants in yeast.

Studies of induction of suppressor mutants may be obscured by revertants already present in the treated population. Such revertants, which appear as a minority of prototrophs among auxotrophs, can be eliminated by pretreatment with nystatin before application of the mutagen. Treatment with nystatin, under the proper conditions, decreased the frequency of prototrophs about 30-fold. This is sufficient for studying induced mutation at frequencies close to the spontaneous frequency.