MS2I6A DEFICIENCY ENHANCES PROOFREADING IN TRANSLATION

The hypermodified base 2-methylthio-N6-isopentenyladenosine (ms2i6A) at position 37 occurs frequently in tRNAs that read codons starting with uridine. Here we have studied how ms2i6A affects the accuracy of poly(U) translation in vitro. Deficiency leads to a higher rejection rate of tRNA4Leu by more aggressive proofreading on the wild-type ribosome, but with the initial selection step unchanged. Our data indicate that ms2i6A has no effect on codon-anticodon interactions on wild-type ribosomes as long as aminoacyl-tRNA is in ternary complex with EF-Tu and GTP. ms2i6A deficiency in the cognate poly(U) reader tRNAPhe leads to increased misreading when the near-cognate competitor tRNA4Leu is wild-type. ms2i6A deficiency in tRNA4Leu gives a decreased error level in competition with wild-type tRNAPhe. © 1991.