Yoon K, Hobbs C A, Walter A E, Turner D H
Department of Molecular Biology, Sterling Winthrop Pharmaceuticals Research Division, Malvern, PA 19355.
Nucleic Acids Res. 1993 Feb 11;21(3):601-6. doi: 10.1093/nar/21.3.601.
An effect of 5'-phosphorylation on the stability of triple helical DNA containing pyrimidine:purine:pyrimidine strands has been demonstrated by both gel electrophoresis and UV melting. A 5'-phosphate on the purine-rich middle strand of a triple helix lowers the stability of triple helix formation by approximately 1 kcal/mol at 25 degrees C. The middle strand is involved in both Watson-Crick and Hoogsteen base pairing. In contrast, a 5'-phosphate on the pyrimidine-rich strands, which are involved in either Watson-Crick or Hoogsteen base pairing, has a smaller effect on the stability of triple helix. The order of stability is: no phosphate on either strand > phosphate on both pyrimidine strands > phosphate on purine strand > phosphate on all three strands. Differential stability of triple helix species is postulated to stem from an increase in rigidity due to steric hindrance from the 5'-phosphate. This result indicates that labelling with 32P affect equilibrium in triplex formation.
通过凝胶电泳和紫外熔解实验均已证明，5'-磷酸化对含有嘧啶：嘌呤：嘧啶链的三链螺旋DNA稳定性具有影响。在三链螺旋富含嘌呤的中间链上的5'-磷酸基团，在25℃时会使三链螺旋形成的稳定性降低约1千卡/摩尔。中间链参与了沃森-克里克碱基对和 hoogsteen 碱基对。相比之下，富含嘧啶的链上的5'-磷酸基团，其参与沃森-克里克或hoogsteen碱基对，对三链螺旋稳定性的影响较小。稳定性顺序为：两条链均无磷酸基团＞两条嘧啶链均有磷酸基团＞嘌呤链有磷酸基团＞三条链均有磷酸基团。三链螺旋物种的差异稳定性被推测源于5'-磷酸基团的空间位阻导致的刚性增加。这一结果表明，用32P标记会影响三链体形成的平衡。
