Chemically induced dynamic nuclear polarization studies of yeast tRNAPhe

Chemically induced dynamic nuclear polarization (CIDNP) has been observed from yeast tRNAPhe following reaction with photoexcited riboflavin. At 20 degrees 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 [ McCord , E.F., Morden , K. M., Pardi , A., Tinoco , I., Jr., & Boxer, S. G. (1984) Biochemistry (preceding paper in this issue)]. The methyl protons of m22G -26 show strong negative spin polarization, indicating that this residue is accessible. The solvent accessibility of this residue has not been previously demonstrated. In addition, two positively polarized aromatic resonances are observed, which are likely due to two or more G(H8) protons, including those of G-20, m22G -26, and/or Gm-34. For temperatures below 50 degrees C, a negatively polarized signal in the aromatic region is shown to arise from cross relaxation with the methyl group protons of m22G -26. This indicates the proximity of an aromatic proton, probably H2 of A-44, to the methyl groups of m22G -26. 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 first 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.