Coexistence of G‐Quadruplex and i‐Motif Within a DNA Duplex is Tolerated by a PCBP2‐Assisted Replisome

作者：Yanling Bao, Shi-Chao Wu, Lijuan Guo, Xiaoxuan Song, Zhiyun Ren, Jiazheng Zhao, Mingyao Wang, Lishuang Chen, Bingkai Cheng, Xi‐Miao Hou, Cong Liu, Yadong Sun, Bo Sun · 发表于：Angewandte Chemie International Edition · 年份：2025 · DOI：10.1002/anie.202523769 · 被引用次数：4 · 研究领域：DNA and Nucleic Acid Chemistry、RNA Interference and Gene Delivery、Advanced biosensing and bioanalysis techniques

Abstract G‐quadruplexes (G4s) and i‐motifs (iMs) are non‐canonical, four‐stranded DNA structures that are formed in guanine‐ and cytosine‐rich sequences, respectively. These structural motifs play crucial regulatory roles in diverse genomic processes and have emerged as promising therapeutic targets. Although individual G4s and iMs have been intensively characterized, whether they could form simultaneously on complementary DNA strands has remained unclear. Using single‐molecule analysis, we demonstrate that under physiologically relevant conditions, G4 and iM structures can indeed coexist within a native DNA fragment comprising 24 guanine and cytosine bases. Strikingly, due to the intrinsic sequence complementation, the stabilities of the two motifs are mutually affected, giving rise to a tightly coupled unfolding pathway. Quantitative measurements reveal that iM unfolding attenuates the mechanical stability of the facing G4 by approximately 13.7 kcal mol −1 . Furthermore, we identify an oncogenic splicing factor, PCBP2, as an iM‐interacting protein. Through destabilizing iM and consequently the concomitant G4, PCBP2 enables a replisome to bypass these otherwise persistent barriers. Our findings provide fresh insights into G4–iM interplay and establish PCBP2 as a key regulator of structured DNA during genome maintenance.