G-Quadruplex and i-Motif Are Mutually Exclusive in ILPR Double-Stranded DNA

详细信息	查看全文 | 推荐本文 |

• 作者：Soma Dhakal ; Zhongbo Yu ; Ryan Konik ; Yunxi Cui ; Deepak Koirala ; Hanbin Mao ; ^{hmao@kent.edu}
• 刊名：Biophysical Journal
• 出版年：2012
• 期刊代码：P13_00063495
• 类别：bio
• 出版时间：6 June, 2012
• 卷：102
• 期：11
• 页码：2575-2584
• 文件大小：981 K

摘要

G-quadruplex has demonstrated its biological functions in聽vivo. Although G-quadruplex in single-stranded DNA (ssDNA) has been well characterized, investigation of this species in double-stranded DNA (dsDNA) lags behind. Here we use chemical footprinting and laser-tweezers-based single-molecule approaches to demonstrate that a dsDNA fragment found in the insulin-linked polymorphic region (ILPR), 5鈥?(ACA GGGG TGT GGGG)₂ TGT, can fold into a G-quadruplex at pH 7.4 with 100聽mM K⁺, and an i-motif at pH 5.5 with 100聽mM Li⁺. Surprisingly, under a condition that favors the formation of both G-quadruplex and i-motif (pH 5.5, 100聽mM K⁺), a unique determination of change in the free energy of unfolding (螖G_unfold) by laser-tweezers experiments provides compelling evidence that only one species is present in each dsDNA. Under this condition, molecules containing G-quadruplex are more stable than those with i-motif. These two species have mechanical stabilities (rupture force 鈮?17 pN) comparable to the stall force of RNA polymerases, which, from a mechanical perspective alone, could justify a regulatory mechanism for tetraplex structures in the expression of human insulin.