EFFECT OF MONOVALENT CATION-INDUCED TELOMERIC DNA-STRUCTURE ON THE BINDING OF OXYTRICHA TELOMERIC PROTEIN
EFFECT OF MONOVALENT CATION-INDUCED TELOMERIC DNA-STRUCTURE ON THE BINDING OF OXYTRICHA TELOMERIC PROTEIN
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DOI：
10.1093/nar/18.15.4543
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发表时间：
1990-08-11
影响因子：
14.9
通讯作者：
CECH, TR
中科院分区：
文献类型：
--
作者：
RAGHURAMAN, MK;CECH, TR
带有 4 个富含端粒脱氧鸟苷序列重复的寡核苷酸经历单价阳离子诱导转变为具有 G-G 碱基对的折叠构象，建模为“G-四重体”结构。我们现在已经推导出 d(TTTTGGGG)4 的折叠和展开速率，该 d(TTTTGGGG)4 具有四个尖毛虫端粒 DNA 序列的重复。在50mM Na+和K+中，37℃下折叠形式的ΔG的估计平均值分别为-2.2kcal/mol和-4.7kcal/mol。完全折叠的 DNA 不被尖毛虫端粒结合蛋白识别；蛋白质结合的底物具有与其部分或完全展开一致的性质。为了证实这一结论，通过甲基化防止 DNA 折叠使得蛋白质在存在单价阳离子的情况下与不存在单价阳离子时一样快速结合。 DNA 的缓慢展开（t1/2 = 4 小时和 18 小时，在 37°C 的 Na+ 和 K+ 中，分别）表明，如果此类结构在体内形成，那么它们将是长期存在的，除非它们可以主动展开。端粒结合蛋白无法结合稳定的、折叠形式的4重复端粒序列是一个可以在体内通过避免四个单链重复来避免的问题。
Oligonucleotides bearing 4 repeats of telomeric deoxyguanosine-rich sequence undergo a monovalent cation-induced transition to a folded conformation with G-G base pairs, modeled as a ''G-quartet'' structure. We have now deduced the rates of folding and unfolding of d(TTTTGGGG)4, which has four repeats of the Oxytricha telomeric DNA sequence. The estimated average values of .DELTA.G for the folded form at 37.degree.C are -2.2 kcal/mol and -4.7 kcal/mol in 50 mM Na+ and K+, respectively. The fully folded DNA is not recognized by the Oxytricha telomere-binding protein; the substrate for protein binding has properties consistent with its being partly or fully unfolded. In confirmation of this conclusion, prevention of DNA folding by methylation enables the protein to bind as rapidly in the presence of monovalent cations as in their absence. The slow unfolding (t1/2 = 4 hr and 18 hr at 37.degree.C in Na+ and K+, respectively) of the DNA suggests that such structures would be long-lived if they formed in vivo, unless they can be actively unfolded. The inability of the telomere-binding protein to bind the stable, folded form of the 4-repeat telomeric sequence is a problem that may be circumvented in vivo by avoiding four single-stranded repeats.