MUTATIONS AT U2555, A TRANSFER RNA-PROTECTED BASE IN 23S RIBOSOMAL-RNA, AFFECT TRANSLATIONAL FIDELITY

A plasmid carrying a mutation in the highly conserved base U2555 in Escherichia coli 23S rRNA was isolated by selecting for suppression of the -1 frameshift mutation trpE91. U2555 is normally protected in chemical footprinting experiments by the aminoacyl residue of A-site-bound tRNA. Substitution of U2555 by adenine or guanine (but not by cytosine) increased readthrough of all three stop codons and +1 and -1 frameshifting. These effects on translational fidelity demonstrate the importance of U2555 for selection of the correct tRNA at the ribosomal A site.