Ho C K, Van Etten J L, Shuman S
Molecular Biology Program, Sloan-Kettering Institute, New York, New York 10021, USA.
J Virol. 1996 Oct;70(10):6658-64. doi: 10.1128/JVI.70.10.6658-6664.1996.
We report that the A103R protein of Chlorella virus PBCV-1 is an mRNA capping enzyme that catalyzes the transfer of GMP from GTP to the 5' diphosphate end of RNA. This is a two-step reaction in which the enzyme first condenses with GTP to form a covalent enzyme-GMP intermediate and then transfers the GMP to an RNA acceptor to form a GpppN cap. Purified recombinant Al03R is a 38-kDa monomer that lacks RNA (guanine-7-) methyltransferase activity. With respect to its size, amino acid sequence, and biochemical properties, A103R is more closely related to the yeast RNA guanylyltransferases than it is to the multifunctional capping enzymes coded for by other large DNA viruses--the poxviruses and African swine fever virus. We surmise that in order to cap its transcripts, PBCV-l must either encode additional 5' processing activities or else rely on the host alga to provide these functions.
我们报道，小球藻病毒PBCV-1的A103R蛋白是一种mRNA加帽酶，它催化GMP从GTP转移至RNA的5'二磷酸末端。这是一个两步反应，在此反应中，该酶首先与GTP缩合形成共价的酶-GMP中间体，然后将GMP转移至RNA受体以形成GpppN帽。纯化的重组A103R是一种38 kDa的单体，缺乏RNA（鸟嘌呤-7-）甲基转移酶活性。就其大小、氨基酸序列和生化特性而言，A103R与酵母RNA鸟苷酸转移酶的关系比与其他大型DNA病毒——痘病毒和非洲猪瘟病毒编码的多功能加帽酶的关系更为密切。我们推测，为了对其转录本进行加帽，PBCV-1要么必须编码额外的5'加工活性，要么依赖宿主藻类来提供这些功能。
