A dominant suppressor has been discovered which suppresses polarity type mutations, noncomplementing ones and those belonging to short nonpolar complementation groups at the ad2 locus of S. cerevisiae. The suppressor translates two types of nonsense previously established at ad2. These data together with theoretical consideration of relationships between nonsense-translating anticodons and different codons make it possible to suggest a mechanism for the observed suppression. According to this mechanism two nonsense types of ad2 are identified as amber and ochre codons.