Shiber M C, Lavelle L, Fossella J A, Fresco J R
Department of Molecular Biology, Princeton University, New Jersey 08544-1014, USA.
Biochemistry. 1995 Nov 7;34(44):14293-9. doi: 10.1021/bi00044a005.
A novel nucleic acid secondary structure, exemplified by d(A(+)-G)10, is formed by an intramolecular, cooperative, acid-induced, coil-->helix transition. The helix is apparently left-handed, lacks base stacking and pairing, and is maintained by hydrogen and ionic bonds between dA+ "side-chain" residues (with electropositive hydrogens -N6H2, -N1+H) and the phosphodiester backbone. Modeling indicates that those dA+ residues lie approximately parallel to the helix axis, interacting with the n-1 backbone phosphates (with electronegative oxygens), somewhat like the -C=O...H-N- longitudinal interactions in a protein alpha-helix. Moreover, the intervening dG side-chain residues are extrahelical, as are amino acid side chains of an alpha-helix.
一种以d(A(+)-G)10为代表的新型核酸二级结构，是由分子内协同的酸诱导卷曲-螺旋转变形成的。该螺旋显然是左手螺旋，缺乏碱基堆积和配对，并且通过dA+“侧链”残基（带有带正电的氢原子-N6H2、-N1+H）与磷酸二酯主链之间的氢键和离子键得以维持。模型表明，那些dA+残基大致平行于螺旋轴，与n-1位的主链磷酸基团（带有带负电的氧原子）相互作用，有点类似于蛋白质α-螺旋中的-C=O...H-N-纵向相互作用。此外，中间的dG侧链残基位于螺旋外，就像α-螺旋的氨基酸侧链一样。
