Akke M, Fiala R, Jiang F, Patel D, Palmer A G
Department of Biochemistry and Molecular Biophysics, Columbia University, New York, New York 10032, USA.
RNA. 1997 Jul;3(7):702-9.
Intramolecular dynamics of guanine and uracil bases in a 14-nt RNA hairpin including the extraordinarily stable UUCG tetraloop were studied by 15N spin relaxation experiments that are sensitive to structural fluctuations occurring on a time scale of picoseconds to nanoseconds. The relaxation data were interpreted in the framework of the anisotropic model-free formalism, using assumed values for the chemical shift anisotropies of the 15N spins. The rotational diffusion tensor was determined to be symmetric with an axial ratio of 1.34 +/- 0.12, in agreement with estimates based on the ratio of the principal moments of the inertia tensor. The model-free results indicate that the bases of the G x U pair in the tetraloop are at least as rigid as the interior base pairs in the stem, whereas the 5'-terminal guanine is more flexible. The observed range of order parameters corresponds to base fluctuations of 19-22 degrees about the chi torsion angle. The results reveal dynamical consequences of the unusual structural features in the UUCG tetraloop and offer insights into the configurational entropy of hairpin formation.
通过对皮秒到纳秒时间尺度上发生的结构波动敏感的15N自旋弛豫实验，研究了包含异常稳定的UUCG四环的14核苷酸RNA发夹中鸟嘌呤和尿嘧啶碱基的分子内动力学。利用15N自旋化学位移各向异性的假定值，在各向异性无模型形式框架内解释弛豫数据。确定旋转扩散张量是对称的，轴比为1.34±0.12，这与基于惯性张量主矩比的估计一致。无模型结果表明，四环中G×U对的碱基至少与茎中的内部碱基对一样刚性，而5'端鸟嘌呤更灵活。观察到的序参量范围对应于围绕χ扭转角19-22度的碱基波动。结果揭示了UUCG四环中异常结构特征的动力学后果，并为发夹形成的构型熵提供了见解。
