Alterations in ribosomal protein RPS28 can diversely affect translational accuracy in Saccharomyces cerevisiae

Three small-subunit ribosomal proteins shown to influence translational accuracy in Saccharomyces cerevisiae are conserved in structure and function with their procaryotic counterparts. One of these, encoded by RPS28A and RPS28B (RPS28), is comparable to bacterial S12. The others, encoded by sup44 (RPS4) or, sup46 and YS11A (RPS13), are homologues of procaryotic S5 and S4, respectively. In Escherichia coli, certain alterations in S12 cause hyperaccurate translation or antibiotic resistance that can be counteracted by other changes in S5 or S4 that reduce translational accuracy. Using site-directed and random mutagenesis, we show that different changes in RPS28 can have diametrical influences on translational accuracy or antibiotic sensitivity in yeast. Certain substitutions in the amino-terminal portion of the protein, which is diverged from the procaryotic homologues, cause varying levels of nonsense suppression or antibiotic sensitivity. Other alterations, found in the more conserved carboxyl-terminal portion, counteract SUP44- or SUP46-associated antibiotic sensitivity, mimicking E. coli results. Although mutations in these different parts of RPS28 have opposite affects on translational accuracy or antibiotic sensitivity, additive phenotypes can be observed when opposing mutations are combined in the same protein.