Venczel E A, Sen D
Department of Chemistry, Simon Fraser University, Burnaby, British Columbia, Canada.
Biochemistry. 1993 Jun 22;32(24):6220-8. doi: 10.1021/bi00075a015.
We investigated the formation in vitro of higher order structures by a DNA oligomer containing the terminal motif TGTG3TGTGTGTG3, derived from the Saccharomyces telomeric consensus, in order to (a) understand why certain cations favor the formation of parallel-stranded (G4 and G8) G-DNA structures, while others favor foldback, antiparallel structures (G'2) and (b) probe the structures of G-DNAs formed by this telomeric sequence, which is more complex than its well-studied counterparts from the protozoans oxytricha and tetrahymena. We find that dramatic switches in the formation of G4 versus G'2 structures occur in solutions of not only the group Ia cations, Li(+)-Cs+, but also in those of the group IIa cations, Mg(2+)-Ba2+. These data and the temperature-dependent formation and destruction of the different structures lend support to the kinetic scheme of Sen and Gilbert (1990), by which rapidly forming G'2 structures accumulate in highly stabilizing potassium (and strontium) solutions at the expense of the thermodynamically more stable G4 structures. Both the G4 and the G'2 complexes formed by the Saccharomyces sequence show novel structural features. Protection and interference experiments with dimethyl sulfate and potassium permanganate reveal that the core of alternating thymines and guanines within the telomeric motif plays a critical role in the stabilization of the parallel G4 structure, but not of the antiparallel G'2. Very likely, in the G4 complex, this GT core forms a novel higher order arrangement of alternating G and T quartets, the latter possibly comparable to the U quartets described by Cheong and Moore (1992) in their NMR study of the higher order structure formed by rUG4U.
我们研究了一种含有末端基序TGTG3TGTGTGTG3的DNA寡聚物在体外形成高阶结构的情况，该基序源自酿酒酵母端粒共有序列，目的是：（a）理解为什么某些阳离子有利于形成平行链（G4和G8）G-DNA结构，而其他阳离子则有利于形成回折的反平行结构（G'2）；（b）探测由该端粒序列形成的G-DNA的结构，该序列比来自原生动物嗜热四膜虫和绿草履虫的已被深入研究的对应序列更为复杂。我们发现，不仅在Ia族阳离子Li(+)-Cs+的溶液中，而且在IIa族阳离子Mg(2+)-Ba2+的溶液中，G4与G'2结构的形成都会发生显著转变。这些数据以及不同结构随温度的形成和破坏情况，支持了森和吉尔伯特（1990年）的动力学方案，即快速形成的G'2结构在高度稳定的钾（和锶）溶液中积累，以热力学上更稳定的G4结构为代价。由酿酒酵母序列形成的G4和G'2复合物都显示出新颖的结构特征。用硫酸二甲酯和高锰酸钾进行的保护和干扰实验表明，端粒基序内交替出现的胸腺嘧啶和鸟嘌呤核心在平行G4结构的稳定中起关键作用，但在反平行G'2结构的稳定中并非如此。很可能，在G4复合物中，这个GT核心形成了一种交替的G和T四联体的新型高阶排列，后者可能类似于张和摩尔（1992年）在对rUG4U形成的高阶结构进行核磁共振研究时所描述的U四联体。
