A TRANSLATIONAL FIDELITY MUTATION IN THE UNIVERSALLY CONSERVED SARCINRICIN DOMAIN OF 25S YEAST RIBOSOMAL-RNA/

Recent evidence suggests that ribosomal RNAs have functional roles in translation. We describe here a new ribosomal RNA mutation that causes translational suppression and antibiotic resistance in eukaryotic cel ls, Using random mutagenesis of the cloned ribosomal RNA gene and in v ivo selection, we isolated a C --> U mutation in the universally conse rved sarcin/ricin domain in Saccharomyces cerevisiae 25S ribosomal RNA . This mutation changes the putative CG pair, which closes the GAGA te traloop in the sarcin/ricin domain, into a weaker UG pair without elim inating ribosomal sensitivity to ricin, We show that suppression of se veral UGA, UAG, and frameshift mutations is evident when a portion of the cellular ribosomal RNA contains the C --> U mutation. Cells that c ontain essentially all mutant ribosomal RNA grow only 10% slower than the wild-type, but show increased suppression as well as resistance to paromomycin, G418, and hygromycin, and sensitivity to cycloheximide. Our results provide genetic evidence for the participation of the sarc in/ricin loop in maintaining translational accuracy and are discussed in terms of a hypothesis that this ribosomal RNA region normally under goes a conformational change during translation.