Gazzani S, Lawrenson T, Woodward C, Headon D, Sablowski R
Cell and Developmental Biology, John Innes Centre, Norwich NR4 7UH, UK.
Science. 2004 Nov 5;306(5698):1046-8. doi: 10.1126/science.1101092.
In RNA interference (RNAi), double-stranded RNA (dsRNA) triggers degradation of homologous messenger RNA. In many organisms, RNA-dependent RNA polymerase (RdRp) is required to initiate or amplify RNAi, but the substrate for dsRNA synthesis in vivo is not known. Here, we show that RdRp-dependent transgene silencing in Arabidopsis was caused by mutation of XRN4, which is a ribonuclease (RNase) implicated in mRNA turnover by means of decapping and 5'-3' exonucleolysis. When both XRN4 and the RdRp were mutated, the plants accumulated decapped transgene mRNA. We propose that mRNAs lacking a cap structure become exposed to RdRp to initiate or maintain RNAi.
在RNA干扰（RNAi）过程中，双链RNA（dsRNA）会引发同源信使RNA的降解。在许多生物体中，RNA依赖的RNA聚合酶（RdRp）是启动或放大RNAi所必需的，但体内dsRNA合成的底物尚不清楚。在此，我们表明拟南芥中RdRp依赖的转基因沉默是由XRN4突变引起的，XRN4是一种核糖核酸酶（RNase），通过脱帽和5'-3'核酸外切作用参与mRNA周转。当XRN4和RdRp都发生突变时，植物会积累脱帽的转基因mRNA。我们提出，缺乏帽结构的mRNA会暴露于RdRp以启动或维持RNAi。
