Wilson T J, Nahas M, Ha T, Lilley D M J
Cancer Research U.K. Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dundee DD1 5EH, UK.
Biochem Soc Trans. 2005 Jun;33(Pt 3):461-5. doi: 10.1042/BST0330461.
The active form of the hairpin ribozyme is brought about by the interaction of two formally unpaired loops. In a natural molecule, these are present on two adjacent arms of a four-way junction. Although activity can be obtained in molecules lacking this junction, the junction is important in the promotion of the folded state of the ribozyme under physiological conditions, at a rate that is faster than the chemical reaction. Single-molecule fluorescence resonance energy transfer studies show that the junction introduces a discrete intermediate into the folding process, which repeatedly juxtaposes the two loops and thus promotes their docking. Using single-molecule enzymology, the cleavage and ligation rates have been measured directly. The pH dependence of the rates is consistent with a role for nucleobases acting in general acid-base catalysis.
发夹状核酶的活性形式是由两个形式上未配对的环相互作用产生的。在天然分子中，它们存在于一个四臂连接体的两个相邻臂上。尽管在缺乏这种连接体的分子中也能获得活性，但该连接体对于在生理条件下促进核酶的折叠状态很重要，其速度比化学反应快。单分子荧光共振能量转移研究表明，该连接体在折叠过程中引入了一个离散的中间体，该中间体反复使两个环并列，从而促进它们的对接。使用单分子酶学，已直接测量了切割和连接速率。速率的pH依赖性与核碱基在一般酸碱催化中发挥作用一致。
