G-四链体是由富含鸟嘌呤的DNA、RNA序列折叠成的具有四条链的高级致密核酸结构。G4 DNA广泛存在于基因启动子和染色体端粒，G4 RNA存在于转录产生的信使RNA和端粒RNA，对端粒的稳定和基因表达起重要调控作用。对G4调控机理的认识将有助于对癌症和衰老现象的理解。在细胞内，高度稳定的G4结构是如何由特异的解旋酶在特定时空状态下来调控的，是一个极具挑战性的研究。G4解旋酶调控的分子机理方面的研究才刚刚起步。在本项目中，我们将借助先进的单分子生物物理手段，特别结合我们发展的单分子磁镊和单分子荧光耦合技术，研究几类重要G4 DNA、RNA解旋酶的微观工作机制，包括酶如何识别G4，酶的移动方向、多聚状态、G4解旋中间过程、ATP驱动的分子马达调控等，并对比G4 DNA和RNA在解旋机理上的差异。本项目的实施，对理解G4结构的物理学基础和生物学功能，推动以G4为靶点的抗癌药物设计具有重要意义。

G-quadruplexes (G4) are highly compact nucleic acids structures formed by Guanine-rich DNA or RNA that fold into a four-stranded conformation. G4 DNA is distributed in gene promoters and chromosome telomere regions while G4 RNA is in messenger RNA and telomere RNA produced by gene and telomere transcription. G4 structures play important roles in the maintenance of telomere stability and regulation of gene expression. Examining G4 structures and their regulation helps our further understanding of cancer and aging. In cells, G4 structures are controlled timely and spatially by a series of highly specific helicases. It is challenging to study G4 unfolding mechanisms by these helicases and the relevant studies are at the very early stage. In this project, we plan to use an advanced single molecule approach, especially the conjugation of magnetic tweezers and single molecule FRET, to study the detailed unfolding mechanisms of several important G4 DNA, RNA helicases. Questions will be examined include how those helicases recognize G4 structures specifically, how helicases translocate on G4, what their oligomeric states and the intermediates of G4 unfolding are, and how ATP functions in regulation of molecular motors et al. We will also compare the differences between G4 DNA and RNA unfolding. Our study will help further understanding of the physical properties and biological functions of G4, and benefit the G4 targeted anti-cancer drug design.