Carbon-13 NMR relaxation studies of pre-melt structural dynamics in [4-13C-uracil] labeled E. coli transfer RNA1Val*

摘要

We report 67.8 MHz carbon-13 spin-lattice relaxation studies on [4-13C-uracil] labeled tRNAVal purified form E. Coli S0-187. following 13 C-enriched C₄ carbonyl resonances from modified and unsubstituted uridines scattered throughtout the polymer backbone enables us to determine dnyamical features in both loop and helical sem regions. The experimental results have ben analyzed in terms of a model of isotropic overall molecular reorientation. “Anomalous” residus for which the experimental data cannot be accounted for in terms of the model provide an assessmetn of local and regional properties. Thus, “native” tRNAVal under physiological conditions of magnesium (10 mM) and temperature (20°–40°C), exhibits the following characteristics; 1) unidines held rigidly in helical stem and teritary interactions display correlation times for rational reorientation of 15–20 nsecs, typical for overall tRNA motion; 2) uridines in loops such as the wobble residue uridine-5-oxyacetic acid (V₃₄) are quite accessible to solvent; moreover V₃₄ and another loop reside, D₁₇, exhibit local mobility; 3) the teritiary interactions involving 4-thio uridine (s4U₈)and A₁₄a and ribothymidine (rT₅₄) and A₅₈ are weakened as temperature increases.