McKinney S A, Tan E, Wilson T J, Nahas M K, Déclais A-C, Clegg R M, Lilley D M J, Ha T
Department of Physics, University of Illinois, Urbana-Champaign, Urbana, IL 61801, USA.
Biochem Soc Trans. 2004 Feb;32(Pt 1):41-5. doi: 10.1042/bst0320041.
Branched helical junctions are common in nucleic acids. In DNA, the four-way junction (Holliday junction) is an essential intermediate in homologous recombination and is a highly dynamic structure, capable of stacking conformer transitions and branch migration. Our single-molecule fluorescence studies provide unique insight into the energy landscape of Holliday junctions by visualizing these processes directly. In the hairpin ribozyme, an RNA four-way junction is an important structural element that enhances active-site formation by several orders of magnitude. Our single-molecule studies suggest a plausible mechanism for how the junction achieves this remarkable feat; the structural dynamics of the four-way junction bring about frequent contacts between the loops that are needed to form the active site. The most definitive evidence for this is the observation of three-state folding in single-hairpin ribozymes, the intermediate state of which is populated due to the intrinsic properties of the junction.
分支螺旋连接在核酸中很常见。在DNA中，四向连接（霍利迪连接体）是同源重组中的一个重要中间体，是一种高度动态的结构，能够进行堆积构象转变和分支迁移。我们的单分子荧光研究通过直接观察这些过程，为霍利迪连接体的能量景观提供了独特的见解。在发夹状核酶中，RNA四向连接是一个重要的结构元件，它能将活性位点的形成提高几个数量级。我们的单分子研究提出了一个合理的机制，说明连接体是如何实现这一非凡壮举的；四向连接的结构动力学导致形成活性位点所需的环之间频繁接触。最确凿的证据是在单链发夹状核酶中观察到三态折叠，其中间状态是由于连接体的固有特性而存在的。
