Formation of Pseudosymmetrical G-Quadruplex and i-Motif Structures in the Proximal Promoter Region of the RET Oncogene

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• 作者：Kexiao Guo ; Alan Pourpak ; Kara Beetz-Rogers ; Vijay Gokhale ; Daekyu Sun ; Laurence H. Hurley
• 刊名：Journal of the American Chemical Society
• 出版年：2007
• 出版时间：August 22, 2007
• 年：2007
• 卷：129
• 期：33
• 页码：10220 - 10228
• 全文大小：574K
• 年卷期：v.129,no.33(August 22, 2007)
• ISSN：1520-5126

文摘

A polypurine (guanine)/polypyrimidine (cytosine)-rich sequence within the proximal promoter regionof the human RET oncogene has been shown to be essential for RET basal transcription. Specifically, theG-rich strand within this region consists of five consecutive runs of guanines, which is consistent with thegeneral motif capable of forming intramolecular G-quadruplexes. Here we demonstrate that, in the presenceof 100 mM K⁺, this G-rich strand has the ability to adopt two intramolecular G-quadruplex structures invitro. Moreover, comparative circular dichroism (CD) and DMS footprinting studies have revealed that the3'-G-quadruplex structure is a parallel-type intramolecular structure containing three G-tetrads. TheG-quadruplex-interactive agents TMPyP4 and telomestatin further stabilize this G-quadruplex structure. Inaddition, we demonstrate that the complementary C-rich strand forms an i-motif structure in vitro, as shownby CD spectroscopy and chemical footprinting. This 19-mer duplex sequence is predicted to form stableintramolecular G-quadruplex and i-motif species having minimum symmetrical loop sizes of 1:3:1 and 2:3:2, respectively. Together, our results indicate that stable G-quadruplex and i-motif structures can formwithin the proximal promoter region of the human RET oncogene, suggesting that these secondary structuresplay an important role in transcriptional regulation of this gene.