Eberle Andrea B, Lykke-Andersen Søren, Mühlemann Oliver, Jensen Torben Heick
Institute of Cell Biology, University of Bern, Baltzerstrasse 4, CH-3012 Bern, Switzerland.
Nat Struct Mol Biol. 2009 Jan;16(1):49-55. doi: 10.1038/nsmb.1530. Epub 2008 Dec 7.
From yeast to humans, mRNAs harboring premature termination codons (PTCs) are recognized and degraded by nonsense-mediated mRNA decay (NMD). However, degradation mechanisms of NMD have been suggested to differ between species. In Drosophila melanogaster, NMD is initiated by endonucleolysis near the PTC, whereas in yeast and human cells the current view posits that NMD occurs by exonucleolysis from one or both RNA termini. Here we report that degradation of human nonsense mRNAs can be initiated by PTC-proximal endonucleolytic cleavage. We identify the metazoan-specific NMD factor SMG6 as the responsible endonuclease by demonstrating that mutation of conserved residues in its nuclease domain--the C-terminal PIN motif--abolishes endonucleolysis in vivo and in vitro. Our data lead to a revised mechanistic model for degradation of nonsense mRNA in human cells and suggest that endonucleolytic cleavage is a conserved feature in metazoan NMD.
从酵母到人类，携带提前终止密码子（PTC）的mRNA会被无义介导的mRNA降解（NMD）识别并降解。然而，有研究表明NMD的降解机制在不同物种间存在差异。在黑腹果蝇中，NMD由PTC附近的核酸内切作用启动，而在酵母和人类细胞中，目前的观点认为NMD是通过从RNA的一个或两个末端进行核酸外切作用发生的。在此，我们报告人类无义mRNA的降解可由PTC近端的核酸内切裂解启动。我们通过证明其核酸酶结构域（C末端PIN基序）中保守残基的突变在体内和体外消除了核酸内切作用，确定后生动物特异性NMD因子SMG6为负责的核酸内切酶。我们的数据为人类细胞中无义mRNA的降解提出了一个修订的机制模型，并表明核酸内切裂解是后生动物NMD中的一个保守特征。
