A Study of The G-Wire DNA by Atomic Force Microscopy

去氧核酸鏈（CCG）_4由胞核鹼基質子化引發自行組合四股核酸鏈之原子力顯微鏡技術研究

林淑萍(Shwu-Bin Lin) ； 方曄(Ye Fang) ； 甘魯生(Lou-Sing Kan)

《中央研究院化學研究所集刊》 45期 (1998/03) Pp. 45-54

https://doi.org/10.6522/BICAS.1998.45.4

摘要

含高成份鳥糞核酸鹼基（G）之核酸可以自行組合成高分子量之G-線，其主要之結構為G-四股核酸鏈。由研究結果得知能否自行組合成G-線是和核酸鏈之鹼基順序及週圍化學環境如酸鹼度和離子強度有闕，田納西大學的陳復明教授研究得知在酸性及濃鉀子之狀態下d（CCG）_4核酸鏈能形成高層次之核酸結構（J. BioI. Chem., (1995), 270, 23090-23096）。本篇就是利用原子力顯微技術（AFM）來觀察在上述情況下之d（CCG）_4結構。我們發現鉀離子在摩爾濃度及酸鹼度5.7情況下，可以慢慢產生不同分子量之高聚合G-線，如果將酸鹼度降低至4.6，高分子之聚合物則大部份變成四股核酸之寡核酸鏈。酸鹼度4.6是非常接近胞核酸鹼基之pKa，所以在N3原子上之質子化可提供另一調制含核酸四股核酸之DNA微結構生成的方法。

並列摘要

The so-called G-wire DNA is a high molecular weight species containing G-quadruplexes by way of self-assembled of guanosine-rich DNA oligomers. The assembly of the G-wire DNA depends strongly on the DNA sequence and its chemical environmental condition, such as pH and cation strength. It has been revealed that d(CGG)_4 can form a novel superstructure facilitated by low pH and concentrated potassium ions (Chen, F.-M. J. BioI. Chem. 1995,270,23090-23096). Using atomic force microscopy (AFM), we investigated the behavior of d(CGG)_4 in solutions and found that under acidic conditions and in the presence of concentrated potassium ions in molar range, it can self-assemble slowly into DNA quadruplexes of varying molecular weights. At pH 5.7, longer G-wire DNA's were formed and exhibited, to some extent, higher aggregates. However, when close to the pKa of deoxycytosine protonation (4.6), the predominant conformations observed were oligomerized species rather than polymerized ones. The controllability of the G-quadruplex polymerization in d(CGG)_4 by protonation on N_3 atom of cytosine may provide an alternate route to regulate the growth of the novel G-quadruplex-based nanostructure of DNA.