Howell R M, Woodford K J, Weitzmann M N, Usdin K
Section on Genomic Structure and Function, Laboratory of Biochemical Pharmacology, NIDDK, National Institutes of Health, Bethesda, Maryland 20892-0830, USA.
J Biol Chem. 1996 Mar 1;271(9):5208-14. doi: 10.1074/jbc.271.9.5208.
We have previously shown that the G-rich sequence G16CG(GGT)2GG in the promoter region of the chicken beta-globin gene poses a formidable barrier to DNA synthesis in vitro (Woodford et al., 1994, J. Biol. Chem. 269, 27029-27035). The K+ requirement, template-strand specificity, template concentration independence, and involvement of Hoogsteen bonding suggested that the underlying basis of this new type of DNA synthesis arrest site might be an intrastrand tetrahelical structure. However, the arrest site lacks the four G-rich repeats that are a hallmark of previously described intramolecular tetraplexes and contains a number of noncanonical bases that would be expected to greatly destabilize such a structure. Here we report evidence for an unusual K+-dependent intrastrand "cinched" tetraplex. This structure has several unique features including the incorporation of bases other than guanine into the stem of the tetraplex, interaction between loop bases and bases in the flanking region, and base pairing between bases 3 and 5 of the tetrahelix-forming region to form a molecular "cinch." This finding extends the range of sequences capable of tetraplex formation as well as our appreciation of the conformational complexity of the chicken beta-globin promoter.
我们先前已经表明，鸡β-珠蛋白基因启动子区域中富含G的序列G16CG(GGT)2GG在体外对DNA合成构成了巨大障碍（Woodford等人，1994年，《生物化学杂志》269卷，27029 - 27035页）。对钾离子的需求、模板链特异性、模板浓度独立性以及Hoogsteen键的参与表明，这种新型DNA合成停滞位点的潜在基础可能是链内四螺旋结构。然而，该停滞位点缺乏作为先前描述的分子内四链体标志的四个富含G的重复序列，并且包含一些非规范碱基，预计这些碱基会极大地破坏这种结构的稳定性。在此，我们报告了一种不寻常的钾离子依赖性链内“收紧”四链体的证据。这种结构具有几个独特特征，包括除鸟嘌呤外的其他碱基掺入四链体的茎中、环碱基与侧翼区域碱基之间的相互作用以及四螺旋形成区域的碱基3和碱基5之间的碱基配对以形成分子“收紧”。这一发现扩展了能够形成四链体的序列范围，也加深了我们对鸡β-珠蛋白启动子构象复杂性的认识。
