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Polynucleotide Ligase Activity of Eukaryotic Topoisomerase I

机译:真核拓扑异构酶I的多核苷酸连接酶活性

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摘要

Introduction of a single ribonucleoside immediately 5' of the scissile phosphate of a duplex DNA substrate converts eukaryotic topoisomerase I into an endoribonuclease. Here, I demonstrate that the RNase reaction is reversible. Vaccinia topoisomerase can ligate 2', 3'-cyclic phosphate and 5'-hydroxyl termini annealed to a bridging template strand. Remarkably, the ligase activity of topoisomerase does not require the active site tyrosine, implying that strand joining can occur via direct attack of the 5' hydroxyl on the cyclic phosphate without a covalent intermediate. Ligation does require other catalytic side chains on the enzyme. these findings underscore how a common ancestral mechanism of phosphoryl and nucleotidyl transfer can be harnessed to perform seemingly diverse tasks through subtle changes at the active site.
机译:立即引入双核DNA底物的易裂磷酸的5'的单个核糖核苷将真核拓扑异构酶I转化为核糖核酸内切酶。在这里,我证明了RNase反应是可逆的。牛痘拓扑异构酶可以连接退火至桥接模板链的2',3'-环磷酸酯和5'-羟基末端。显着地,拓扑异构酶的连接酶活性不需要活性位点酪氨酸,这意味着可以通过在没有共价中间体的情况下通过直接攻击环状磷酸酯上的5'羟基来发生链连接。连接确实需要酶上的其他催化侧链。这些发现强调了如何利用磷酰基和核苷酸基转移的共同祖先机制通过活性位点的细微变化来执行看似多样化的任务。

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