Effects of anticodon 2 '-O-methylations on tRNA codon recognition in an Escherichia coli cell-free translation

The methylation of 2-hydroxyl groups is one of the most common posttranscri ptional modifications of naturally occurring stable RNA molecules. Some tRN A species have a 2'-O-methyl nucleoside at the first position of the antico don, and it was suggested that this modification stabilizes the codon-antic odon duplex. However, no tRNA species have been found to have the modificat ion at the second or third position of the anticodon. In the present study, we measured the effects of anticodon 2-O-methylation on the codon-reading efficiencies of the anticodon variants of the unmodified forms of Escherich ia coli tRNA(1)(Ser), using a cell-free protein synthesis assay. The modifi cation of C in the first position of the anticodon into 2'-O-methylcytidine increased the efficiency of reading the G-ending codon. On the other hand, the modifications of the second and/or third positions were detrimental to the codon-reading activity. Thus, 2'-hydroxyl groups at the second and thi rd positions of the anticodon may have some role in the translation reactio n, and this may be the reason why 2'-O-methyl nucleosides are not found in these positions within natural tRNA species.