Fujimura T, Ribas J C, Makhov A M, Wickner R B
Departamento de Microbiología y Genética, CSIC/Universidad de Salamanca, Spain.
Nature. 1992 Oct 22;359(6397):746-9. doi: 10.1038/359746a0.
Double-stranded RNA viruses have an RNA-dependent RNA polymerase activity associated with the viral particles which is indispensable for their replication cycle. Using the yeast L-A double-stranded RNA virus we have investigated the mechanism by which the virus encapsidates its genomic RNA and RNA polymerase. The L-A gag gene encodes the principal viral coat protein and the overlapping pol gene is expressed as a gag-pol fusion protein which is formed by a -1 ribosomal frameshift. Here we show that Gag alone is sufficient for virus particle formation, but that it fails to package the viral single-stranded RNA genome. Encapsidation of the viral RNA requires only a part of the Pol region (the N-terminal quarter), which is presumably distinct from the RNA polymerase domain. Given that the Pol region has single-stranded RNA-binding activity, these results are consistent with our L-A virus encapsidation model: the Pol region of the fusion protein binds specifically to the viral genome (+) strand, and the N-terminal gag-encoded region primes polymerization of Gag to form the capsid, thus ensuring the packaging of both the viral genome and the RNA polymerase.
双链RNA病毒具有与病毒颗粒相关的RNA依赖性RNA聚合酶活性，这对其复制周期至关重要。利用酵母L-A双链RNA病毒，我们研究了该病毒包裹其基因组RNA和RNA聚合酶的机制。L-A gag基因编码主要的病毒衣壳蛋白，重叠的pol基因作为gag-pol融合蛋白表达，该融合蛋白由-1核糖体移码形成。在这里我们表明，单独的Gag足以形成病毒颗粒，但它无法包裹病毒单链RNA基因组。病毒RNA的包裹仅需要Pol区域的一部分（N端四分之一），这可能与RNA聚合酶结构域不同。鉴于Pol区域具有单链RNA结合活性，这些结果与我们的L-A病毒包裹模型一致：融合蛋白的Pol区域特异性结合病毒基因组（+）链，N端gag编码区域引发Gag聚合以形成衣壳，从而确保病毒基因组和RNA聚合酶的包裹。
