Amir-Aslani A, Mauffret O, Bittoun P, Sourgen F, Monnot M, Lescot E, Fermandjian S
Départment de Biologie et Pharmacologie Structurales, CNRS URA 147, Institut Gustave Roussy, Villejuif, France.
Nucleic Acids Res. 1995 Oct 11;23(19):3850-7. doi: 10.1093/nar/23.19.3850.
1H- and 31P-NMR and UV-absorption studies were carried out with the oligonucleotide strands d(AGCT-TATC-ATC-GATAAGCT) (-ATC-) and d(AGCTTATC-GAT-GATAAGCT) (-GAT-) contained in the strongest and salt resistant cleavage site for topoisomerase II in pBR322 DNA. We found that the two oligonucleotides were stabilized under a hairpin structure characterized by a eight base pair stem and a three base loop at low DNA and salt concentrations. In such experimental conditions, only the -GAT- oligonucleotide displayed a partial homoduplex structure in slow equilibrium with its folded structure. Temperature dependencies of imino protons showed that the partial homoduplex of -GAT- melted at a lower temperature than the hairpin structure. It was suggested that the appearance of the partial homoduplex in -GAT- is related to the formation of two stabilizing (G.T) mismatched base pairs in the central loop of this structure. Finally, it was inferred from the dispersion of chemical shifts in the 31P-NMR spectra that the distortions affecting the backbone of the hairpin loop are larger in the case of -ATC- compared with -GAT-. At the same time NOEs proved that the base stacking was stronger within the loop of the -ATC- hairpin.
对pBR322 DNA中拓扑异构酶II最强且耐盐的切割位点所含的寡核苷酸链d(AGCT - TATC - ATC - GATAAGCT) (- ATC -)和d(AGCTTATC - GAT - GATAAGCT) (- GAT -)进行了¹H - 和³¹P - NMR以及紫外吸收研究。我们发现，在低DNA和盐浓度下，这两种寡核苷酸在以八个碱基对的茎和三个碱基的环为特征的发夹结构下是稳定的。在这样的实验条件下，只有 - GAT - 寡核苷酸呈现出与其折叠结构处于缓慢平衡的部分同源双链结构。亚氨基质子的温度依赖性表明， - GAT - 的部分同源双链在比发夹结构更低的温度下解链。有人提出， - GAT - 中部分同源双链的出现与该结构中心环中两个稳定的(G.T)错配碱基对的形成有关。最后，从³¹P - NMR谱中化学位移的分散情况推断，与 - GAT - 相比， - ATC - 的发夹环主链受到的扭曲更大。同时，NOEs证明， - ATC - 发夹环内的碱基堆积更强。
