Khan Nasiruddin, Aviñó Anna, Tauler Romà, González Carlos, Eritja Ramon, Gargallo Raimundo
Department of Analytical Chemistry, University of Barcelona, Diagonal 647, E-08028 Barcelona, Spain.
Biochimie. 2007 Dec;89(12):1562-72. doi: 10.1016/j.biochi.2007.07.026. Epub 2007 Aug 6.
The 5'-end of the P1 promoter of the B-cell lymphoma-2 (bcl-2) gene contains a highly guaninecytosine-rich region, which has a role in the regulation of bcl-2 transcription. Whereas the guanine-rich region has been the focus of recent studies, little attention has been paid to the cytosine-rich strand. Here we examine the structural transitions of the cytosine-rich sequence by means of acid-base, mole-ratio and melting experiments monitored by molecular absorption, circular dichroism, and NMR spectroscopies. Two intramolecular i-motif structures have been detected in the pH range 2-7, with maximal formation at pH 4 and 6, respectively. At pH 7.6 the majority species has been associated with a hairpin involving Watson-Crick base pairs. Upon addition of the quadruplex-interacting ligand TmPyP4, bcl-2c structures at pH 6.1 and 7.6 yield identical interaction species with stoichiometries 1:2 (DNA:ligand) and logarithms of formation constant 12.4+/-0.2 and 11.7+/-0.1, respectively. The initial i-motif structure at pH 6.1 is lost upon interaction with TmPyP4.
B细胞淋巴瘤-2（bcl-2）基因P1启动子的5'端含有一个高度富含鸟嘌呤-胞嘧啶的区域，该区域在bcl-2转录调控中发挥作用。尽管富含鸟嘌呤的区域一直是近期研究的重点，但富含胞嘧啶的链却很少受到关注。在这里，我们通过酸碱、摩尔比和熔解实验，利用分子吸收、圆二色性和核磁共振光谱进行监测，研究了富含胞嘧啶序列的结构转变。在pH值为2至7的范围内检测到两种分子内i-基序结构，分别在pH 4和6时形成最大化。在pH 7.6时，大多数物种与涉及沃森-克里克碱基对的发夹结构相关。加入四链体相互作用配体TmPyP4后，pH 6.1和7.6时的bcl-2c结构产生化学计量比为1:2（DNA:配体）且形成常数对数分别为12.4±0.2和11.7±0.1的相同相互作用物种。pH 6.1时最初的i-基序结构在与TmPyP4相互作用后消失。
