MUTATIONS IN RNAS OF BOTH RIBOSOMAL-SUBUNITS CAUSE DEFECTS IN TRANSLATION TERMINATION

Mutations in RNAs of both subunits of the Escherichia coil ribosome ca used defects in catalysis of peptidyl-tRNA hydrolysis in a realistic i n vitro termination system. Assaying the two codon-dependent cytoplasm ic proteins that drive termination, RF1 and RF2, we observed large def ects with RF2 but not with RF1, a result consistent with the in vivo p roperties of the mutants. Our study presents the first direct in vitro evidence demonstrating the involvement of RNAs from both the large an d the small ribosomal subunits in catalysis of peptidyl-tRNA hydrolysi s during termination of protein biosynthesis. The results and conclusi ons are of general significance since the rRNA nucleotides studied hav e been virtually universally conserved throughout evolution. Our findi ngs suggest a novel role for rRNAs of both subunits as molecular trans mitters of a signal for termination.