The conformation of the anticodon loop of Escherichia coli tRNAArg was investigated. It is shown that the structure of the anticodon loop is influenced by the base composition of the anticodon stem, and the natural modification of the nucleoside residue 32 in the anticodon loop. The structural effects detected by analysis of the accessibility of the anticodon loop to nuclease S1 could be correlated with the ability of different Arg-tRNAArg species to suppress frame-shifting during translation of MS2 RNA.