Hydrogen-bonded protons in the tertiary structure of yeast tRNAPhe in solution.

Abstract

Temperature-dependent lowfield proton magnetic resonance spectra of yeast tRNAPhe were recorded between 10 and 15 parts per million. Seven resonances of hydrogen-bonded protons disappeared reversibly under two sets of conditions where the selective broadening of tertiary structure resonances were predicted by temperature jump experiments. The seven resonances were assigned to the seven tertiary hydrogen bonds expected between 10 and 15 parts per million from the crystal structure of yeast tRNAPhe. Some of the non-Watson-Crick base pairs have unusual unshifted standard chemical shifts after the ring current contributions calculated from the crystal coordinates were subtracted. The differences of the chemical shifts of homologous tertiary structure base pairs in Escherichia coli tRNAfMet and yeast tRNAPhe give experimental evidence for details of the conformational differences postulated by model building on the basis of the x-ray coordinates of yeast tRNAPhe and sequence homologies.