Cheng Chi-Ping, Serviene Elena, Nagy Peter D
Department of Plant Pathology, University of Kentucky, Plant Science Building, Lexington, Kentucky 40546, USA.
J Virol. 2006 Mar;80(6):2631-40. doi: 10.1128/JVI.80.6.2631-2640.2006.
RNA viruses of humans, animals, and plants evolve rapidly due to mutations and RNA recombination. A previous genome-wide screen in Saccharomyces cerevisiae, a model host, identified five host genes, including XRN1, encoding a 5'-3' exoribonuclease, whose absence led to an approximately 10- to 50-fold enhancement of RNA recombination in Tomato bushy stunt virus (E. Serviene, N. Shapka, C. P. Cheng, T. Panavas, B. Phuangrat, J. Baker, and P. D. Nagy, Proc. Natl. Acad. Sci. USA 102:10545-10550, 2005). In this study, we found abundant 5'-truncated viral RNAs in xrn1delta mutant strains but not in the parental yeast strains, suggesting that these RNAs might serve as recombination substrates promoting RNA recombination in xrn1delta mutant yeast. This model is supported by data showing that an enhanced level of viral recombinant accumulation occurred when two different 5'-truncated viral RNAs were expressed in the parental and xrn1delta mutant yeast strains or electroporated into plant protoplasts. Moreover, we demonstrate that purified Xrn1p can degrade the 5'-truncated viral RNAs in vitro. Based on these findings, we propose that Xrn1p can suppress viral RNA recombination by rapidly removing the 5'-truncated RNAs, the substrates of recombination, and thus reducing the chance for recombination to occur in the parental yeast strain. In addition, we show that the 5'-truncated viral RNAs are generated by host endoribonucleases. Accordingly, overexpression of the Ngl2p endoribonuclease led to an increased accumulation of cleaved viral RNAs in vivo and in vitro. Altogether, this paper establishes that host ribonucleases and host-mediated viral RNA turnover play major roles in RNA virus recombination and evolution.
人类、动物和植物的RNA病毒由于突变和RNA重组而迅速进化。先前在模式宿主酿酒酵母中进行的全基因组筛选鉴定出五个宿主基因，包括编码5'-3'外切核糖核酸酶的XRN1，缺失该基因会导致番茄丛生矮化病毒的RNA重组增强约10至50倍（E. Serviene、N. Shapka、C. P. Cheng、T. Panavas、B. Phuangrat、J. Baker和P. D. Nagy，《美国国家科学院院刊》102:10545-10550，2005年）。在本研究中，我们在xrn1delta突变株中发现了大量5'-截短的病毒RNA，而在亲本酵母菌株中未发现，这表明这些RNA可能作为重组底物促进xrn1delta突变酵母中的RNA重组。当两种不同的5'-截短病毒RNA在亲本和xrn1delta突变酵母菌株中表达或电穿孔导入植物原生质体时，病毒重组体积累水平增强的数据支持了这一模型。此外，我们证明纯化的Xrn1p可以在体外降解5'-截短的病毒RNA。基于这些发现，我们提出Xrn1p可以通过快速去除5'-截短的RNA（重组底物）来抑制病毒RNA重组，从而减少亲本酵母菌株中发生重组的机会。此外，我们表明5'-截短的病毒RNA是由宿主内切核糖核酸酶产生的。因此，Ngl2p内切核糖核酸酶的过表达导致体内和体外切割的病毒RNA积累增加。总之，本文证实宿主核糖核酸酶和宿主介导的病毒RNA周转在RNA病毒重组和进化中起主要作用。
