ALTERATIONS IN RIBOSOMAL-PROTEIN RPS28 CAN DIVERSELY AFFECT TRANSLATIONAL ACCURACY IN SACCHAROMYCES-CEREVISIAE

Three small-subunit ribosomal proteins shown to influence translationa l 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 o f procaryotic S5 and S4, respectively. In Escherichia coli, certain al terations in S12 cause hyperaccurate translation or antibiotic resista nce 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 d iverged from the procaryotic homologues, cause varying levels of nonse nse suppression or antibiotic sensitivity. Other alterations, found in the more conserved carboxyl-terminal portion, counteract SUP44- or SU P46-associated antibiotic sensitivity, mimicking E. coli results. Alth ough mutations in these different parts of RPS28 have opposite affects on translational accuracy or antibiotic sensitivity, additive phenoty pes can be observed when opposing mutations are combined in the same p rotein.