Dong Hongping, Ren Suping, Li Hongmin, Shi Pei-Yong
Wadsworth Center, New York State Department of Health, USA.
Virology. 2008 Jul 20;377(1):1-6. doi: 10.1016/j.virol.2008.04.026. Epub 2008 May 23.
West Nile virus methyltransferase catalyzes N7 and 2'-O methylations of the viral RNA cap (GpppA-RNA-->m(7)GpppAm-RNA). The two methylation events are independent, as evidenced by efficient N7 methylation of GpppA-RNA-->m(7)GpppA-RNA and GpppAm-RNA-->m(7)GpppAm-RNA, and by the 2'-O methylation of GpppA-RNA-->GpppAm-RNA and m(7)GpppA-RNA-->m(7)GpppAm-RNA. However, the 2'-O methylation activity prefers substrate m(7)GpppA-RNA to GpppA-RNA, thereby determining the dominant methylation pathway as GpppA-RNA-->m(7)GpppA-RNA-->m(7)GpppAm-RNA. Mutant enzymes with different methylation defects can trans complement one another in vitro. Furthermore, sequential treatment of GpppA-RNA with distinct methyltransferase mutants generates fully methylated m(7)GpppAm-RNA, demonstrating that separate molecules of the enzyme can independently catalyze the two cap methylations in vitro.
西尼罗河病毒甲基转移酶催化病毒RNA帽的N7和2'-O甲基化（GpppA-RNA→m(7)GpppAm-RNA）。这两个甲基化事件是独立的，GpppA-RNA→m(7)GpppA-RNA和GpppAm-RNA→m(7)GpppAm-RNA的高效N7甲基化以及GpppA-RNA→GpppAm-RNA和m(7)GpppA-RNA→m(7)GpppAm-RNA的2'-O甲基化都证明了这一点。然而，2'-O甲基化活性对底物m(7)GpppA-RNA的偏好高于GpppA-RNA，从而确定了主要的甲基化途径为GpppA-RNA→m(7)GpppA-RNA→m(7)GpppAm-RNA。具有不同甲基化缺陷的突变酶在体外可以相互反式互补。此外，用不同的甲基转移酶突变体对GpppA-RNA进行顺序处理可产生完全甲基化的m(7)GpppAm-RNA，这表明该酶的不同分子在体外可以独立催化帽的两种甲基化。
