Mukerji I, Shiber M C, Fresco J R, Spiro T G
Department of Chemistry, Princeton University, NJ 08544-1014, USA.
Nucleic Acids Res. 1996 Dec 15;24(24):5013-20. doi: 10.1093/nar/24.24.5013.
The structure of the oligonucleotide d(A-G)10 in 0.6 M Na+, pH 7.0 has been investigated with UV resonance Raman (UVRR) spectroscopy. Variable wavelength excitation was used to distinguish the spectral contributions of dG and dA residues. Both classes of residues show UVRR hyperchromism with increasing temperature, reflecting unstacking of the bases. The dG residues melt relatively cooperatively with a Tm of approximately 42 degrees C. Unstacking is non-cooperative for the dA residues, increasing linearly between 4 and 80 degrees C. G-tetrads at low temperature are indicated by UVRR frequency shifts of modes associated with C6=O and C2-NH2 of the dG residues, and of vibrations involving N7, all sites of H-bonding. However, there are no indications of interbase H-bonds for the dA residues, showing they do not form H-bonded tetrads. Most of the bases are oriented anti about the glycosyl bond, but at 4 degrees C a fraction of the residues are syn. These results, together with the findings by Shiber et al. [Shiber,M.C., Braswell,E.H., Klump,H. and Fresco,J.R. (1996) Nucleic Acids Res. 24, 5004-5012] that d(A-G)10 under comparable conditions has the molecular weight of a dimer, support a model in which two hairpins interact to form a helical structure with G-tetrads and intercalated dA residues.
利用紫外共振拉曼（UVRR）光谱研究了在0.6 M Na⁺、pH 7.0条件下寡核苷酸d(A - G)₁₀的结构。采用可变波长激发来区分dG和dA残基的光谱贡献。两类残基均随温度升高呈现UVRR增色现象，反映出碱基堆积的破坏。dG残基相对协同地解链，熔解温度（Tm）约为42℃。dA残基的解堆积是非协同的，在4至80℃之间呈线性增加。低温下的G - 四联体由与dG残基的C6 = O和C2 - NH₂相关的模式以及涉及N7（所有氢键位点）的振动的UVRR频移表明。然而，没有迹象表明dA残基存在碱基间氢键，这表明它们不形成氢键四联体。大多数碱基围绕糖苷键呈反式取向，但在4℃时一小部分残基是顺式的。这些结果，连同Shiber等人[Shiber, M.C., Braswell, E.H., Klump, H.和Fresco, J.R. (1996) Nucleic Acids Res. 24, 5004 - 5012]的发现，即在可比条件下d(A - G)₁₀具有二聚体的分子量，支持了一个模型，其中两个发夹相互作用形成具有G - 四联体和插入dA残基的螺旋结构。
