Conformation of charged and uncharged tRNA.

The effect of aminoacylation on the conformation of yeast tRNA(Phe) was investigated by high-resolution (300 MHz) proton nuclear magnetic resonance (NMR) spectroscopy. Resonances in the low-field (-11 to -15 ppm) region of the spectra are due to ring NH protons of Watson-Crick base pairs, and to a very high degree of approximation (within 0.05 ppm) the low-field spectra of tRNA(Phe) and phenylalanyl-tRNA(Phe) are identical. From this observation and analysis of the low-field NMR spectra we conclude that the secondary structures of the two tRNAs are identical with respect to base-pairing schemes and interbase distances in the helical region (0.1-0.2 A). Several tertiary structural features, including conformation of the dihydro-U loop, conformation of the minor loop, relative orientations of the acceptor and the TPsiC stems, dihydro-U and anticodon stems, and probably conformation of the anticodon loop are shown to be the same in tRNA(Phe) and phenylalanyl-tRNA(Phe). Our results leave little remaining opportunity for changes in tertiary structure that would not have been observed by the NMR method.