Nuclear magnetic resonance studies on transfer ribonucleic acid: assignment of AU tertiary resonances

Abstract
The H--bonded ring NH NMR spectra of several tRNA species were examined with particular emphasis on the extreme low-field portion. Between -13.8 and -15 ppm there are 2 extra resonances which are not derived from cloverleaf base pairs. A combined approach involving undermodified tRNA, chemical modification and hairpin fragment studies assigned the T54-A58 resonance at -14.3 ppm in yeast tRNAPhe and Escherichia coli tRNA1Val; the U8-A14 resonance was assigned at -14.3 ppm and the s4U8-A14 resonance in bacterial tRNA was assigned at -14.9 ppm. The T54-A58 resonance shifts between -14.3 and -13.8 ppm depending on the surrounding nucleotide sequence in the ribothymidine loop.