Chemically induced dynamic nuclear polarization studies of yeast tRNAPhe

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Abstract
Chemically induced dynamic nuclear polarization (CIDNP) was observed from yeast tRNAPhe following reaction with photoexcited riboflavin. At 20.degree. C, several resonances of tRNA in the native form show polarization; previous work predicts that only guanosine and its derivatives in single-stranded regions are likely to become polarized. The methyl protons of .**GRAPHIC**. show strong negative spin polarization, indicating that this residue is accessible. The solvent accessibility of this residue was not previously demonstrated. In addition, 2 positively polarized aromatic resonances are observed, which are probably due to .gtoreq. 2 G(H8) protons, including those of G-20, .**GRAPHIC**. and/or Gm-34. For temperatures below 50.degree. C, a negatively polarized signal in the aromatic region arises from cross relaxation with the methyl group protons of .**GRAPHIC**. This indicates the proximity of an aromatic proton, probably H2 of A-44, to the methyl groups of .**GRAPHIC**. At higher temperatures, the CIDNP spectra show polarization of several additional G resonances, including those of m2G-10. These changes in the CIDNP spectra reflect melting of the tertiary and secondary structure of the tRNA. This work is the 1st use of CIDNP to study a large nucleic acid molecule and exemplifies the value of this technique in probing single-stranded and solvent-accessible regions of tRNA.

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