Mitas M, Yu A, Dill J, Haworth I S
Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater 74078, USA.
Biochemistry. 1995 Oct 3;34(39):12803-11. doi: 10.1021/bi00039a041.
To investigate potential structures of d(CGG/CCG)n that might relate to their biological function and association with triplet repeat expansion diseases (TREDs), electrophoretic mobility, chemical modification, and P1 nuclease studies were performed with a single-stranded (ss) oligonucleotide containing (CGG)15 [ss(CGG)15]. The results suggest that ss(CGG)15 forms a hairpin with the following features: (i) a stem containing Gsyn. Ganti base pairs; (ii) at > or = 200 mM K+, CGG repeats on the 5' portion of the stem base-paired to GCG repeats on the 3' side (referred to as the (b) alignment); and (iii) heat stability (Tm = 75 degrees C in low ionic strength). At < or = 100 mM K+, dimethyl sulfate reactions indicated that the hairpin in the (b) alignment was in equilibrium with another structure, presumably a hairpin in the alternative (a) alignment (CGG repeats on the 5' portion of the stem base-paired to CGG repeats on the 3' portion of the stem). Molecular dynamics simulations suggested that the loop region of the (a) alignment contained two guanines stacked on top of one another. The same guanines in the (b) alignment were base-paired in a syn-anti arrangement. We propose that the stability of the loop partially determines the stem alignment.
为了研究可能与其生物学功能以及与三联体重复扩增疾病（TREDs）相关的d(CGG/CCG)n的潜在结构，我们使用含有（CGG）15的单链（ss）寡核苷酸[ss(CGG)15]进行了电泳迁移率、化学修饰和P1核酸酶研究。结果表明，ss(CGG)15形成了一个具有以下特征的发夹结构：（i）一个含有Gsyn.Ganti碱基对的茎；（ii）在K+浓度≥200 mM时，茎5'部分的CGG重复序列与3'侧的GCG重复序列碱基配对（称为（b）排列）；（iii）热稳定性（在低离子强度下Tm = 75℃）。在K+浓度≤100 mM时，硫酸二甲酯反应表明，（b）排列中的发夹结构与另一种结构处于平衡状态，推测是另一种（a）排列中的发夹结构（茎5'部分的CGG重复序列与茎3'部分的CGG重复序列碱基配对）。分子动力学模拟表明，（a）排列的环区域包含两个相互堆叠的鸟嘌呤。（b）排列中相同的鸟嘌呤以syn-anti排列方式碱基配对。我们提出，环的稳定性部分决定了茎的排列。
