Paramagnetic ion effects on the nuclear magnetic resonance spectrum of transfer ribonucleic acid: assignment of the 15-48 tertiary resonance

Abstract

The effects of Co2+ and Mn2+ ions on the low-field NMR spectra of pure [Escherichia coli] class 1 transfer ribonucleic acid (tRNA) species were studied. With 1.2 mM tRNA in the presence of 15 mM MgCl2 discrete paramagnetic effects were observed for Co2+ at concentrations in the range 0.02-0.1 mM and for Mn2+ in the range 0.002-0.01 mM, indicating fast exchange of these cations with tRNA. Both cations paramagnetically relax the s4U8-A14 resonance as well as other resonances from proximal base pairs. The Co2+ site appears to be the same site on G15 which was observed crystallographically; the initially occupied tight Mn2+ site is the cation site involving the phosphate of U8. There are 3 base pairs within 10 .ANG. of both sites: G15-C48, A14-s4U8 and C13-G22; this led to the assignment of the G15-C48 and C13-G22 resonances in the NMR spectrum.