Genetic and biochemical characterization of antisuppressor mutants in the yeast Saccharomyces cerevisiae.

Five mutants carrying antisuppressors which reduce the efficiency of SUP46 suppressor of the yeast, Saccharomyces cerevisiae, were isolated. One of them was found to have an altered protein, S27, of 40S ribosomal subunit by using two-dimensional gel electrophoresis. A single recessive gene, designated asu11, was responsible for the mutation, and the heterodiploid (asu11/+) strain was shown to contain both altered and normal S27 proteins, suggesting that the asu11 locus codes for the S27 protein. The mutant was resistant to an aminoglycoside antibiotic, paromomycin which has been known to induce translational errors. These results together with the previous finding that SUP46 suppressor mutant contains an altered S11 ribosomal protein (Ishiguro et al. 1981) suggest that the secondary mutation in the ribosomal protein, S27, renders the restrictive effect to increased translational ambiguity caused by the alteration of S11 protein.