A HIGHLY SENSITIVE PROBE FOR GUANINE N7 IN FOLDED STRUCTURES OF RNA -APPLICATION TO TRANSFER RNA(PHE) AND TETRAHYMENA GROUP-I INTRON

A nickel complex has been shown to promote conformation-specific oxida tion of guanosine in polynucleotide RNA. In all cases, reaction was st rictly dependent on the solvent exposure and surface properties of gua nine N7. Modification of native tRNA(Phe) (yeast) was detected at G18, G19, G20, and Gm34 and concurred with predictions based on its crysta l structure. Additional guanine derivatives became exposed to oxidatio n only after the tRNA unfolded in the absence of Mg2+. Reaction of the Tetrahymena group I intron RNA (L-21 ScaI) also compared favorably to its three-dimensional model by appropriately identifying guanosine re sidues in hairpin loops, duplex termini, and the essential cofactor bi nding site. These results complemented prior data generated by hydroxy l radical, and in combination they served to distinguish the solvent a ccessibility of sugar backbone and base positions in guanosine residue s. Most importantly, this nickel complex exhibited greater selectivity than either dimethyl sulfate or RNase T1 for characterizing tRNA(Phe) and intron RNA.