NMR studies of ion binding to Escherichia coli tRNAPhe

The effects of magnesium, spermine, and temperature on the conformation of Escherichia coli tRNAPhe have been examined by proton and phosphorus nuclear magnetic resonance spectroscopy. In the low-field proton NMR spectra we have characterized two slowly interconverting conformations of this tRNA at low magnesium ion concentrations. The relative proportion of the conformers is ion dependent but not ion specific. Magnesium affects protons in all the stems of tRNA while spermine effects are localized near the s4U-8-A-14 and G-15-C-48 tertiary bonds. The effects seen in the proton NMR spectra are compared and correlated with those observed in the phosphorus spectra to give assignments of some of the resolved signals from the phosphate groups. The phosphorus spectra are compared with those of yeast tRNAPhe [Gorenstein, D. G., Goldfield, E. M., Chen, R., Kovar, K., & Luxon, B. A. (1981) Biochemistry 20, 2141; Salemink, P. J. M., Reijerse, E. J., Mollevanger, L., & Hilbers, C. W. (1981) Eur. J. Biochem. 115, 635], and the ion effects are discussed with reference to the magnesium and spermine sites found in the crystal structures of yeast tRNAPhe [Holbrook, S. R., Sussman, J. L., Warrant, R. W., Church, G. M., & Kim, S.-H. (1977) Nucleic Acids Res. 4, 2811; Quigley, G. J., Teeter, M. M., & Rich, A. (1978) Proc. Natl. Acad. Sci. U.S.A. 75, 64; Jack, A., Ladner, J. E., Rhodes, D., Brown, R. S., & Klug, A. (1977) J. Mol. Biol. 111, 315].