Zhou Jun, Wei Chunying, Jia Guoqing, Wang Xiuli, Feng Zhaochi, Li Can
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China.
Mol Biosyst. 2010 Mar;6(3):580-6. doi: 10.1039/b919600e. Epub 2009 Dec 14.
It is well known that oligonucleotides containing tracts cytosines can form i-motif structures under acidic conditions (pH < 7). However, whether i-motif can be formed under normal physiological cellular conditions (pH 7.0-7.5) is yet no conclusive proof. In the present work, using circular dichroism (CD), UV absorption spectroscopies and native polyacrylamide gel electrophoresis (PAGE), we provided the compelling evidence for the formation of i-motif structures by four cytosine clusters, C(3)TA(2)C(3) (HT), C(4)GC(4)TA (RET), C(2)T(3)C(2)T(4)C(2)T(3)C(2) (CTC) and GC(2)GC(3)A(4)C(6)G (Rb), at neutral and slightly alkaline pH at 4 degrees C. Furthermore, for HT, we also supplied the evidence for the formation of i-motif structure by fluorescence resonance energy transfer (FRET) and investigated its folding kinetics. The formation time constants obtained by CD and fluorescence experiments are 214 and 493 s, respectively, indicating that HT can slowly form i-motif structure at pH 7.0 and 4 degrees C. This work implies that i-motif structures may possible form in vivo.
众所周知，含有胞嘧啶序列的寡核苷酸在酸性条件（pH < 7）下可形成i-基序结构。然而，在正常生理细胞条件（pH 7.0 - 7.5）下是否能形成i-基序尚无确凿证据。在本研究中，我们使用圆二色性（CD）、紫外吸收光谱和天然聚丙烯酰胺凝胶电泳（PAGE），为四个胞嘧啶簇C(3)TA(2)C(3)（HT）、C(4)GC(4)TA（RET）、C(2)T(3)C(2)T(4)C(2)T(3)C(2)（CTC）和GC(2)GC(3)A(4)C(6)G（Rb）在4℃中性和微碱性pH条件下形成i-基序结构提供了有力证据。此外，对于HT，我们还通过荧光共振能量转移（FRET）提供了其形成i-基序结构的证据，并研究了其折叠动力学。通过CD和荧光实验获得的形成时间常数分别为214和493秒，表明HT在pH 7.0和4℃时可缓慢形成i-基序结构。这项工作表明i-基序结构可能在体内形成。
