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首页> 外文期刊>Molecular and Cellular Biology >Yeast mRNA cap methyltransferase is a 50-kilodalton protein encoded by an essential gene.
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Yeast mRNA cap methyltransferase is a 50-kilodalton protein encoded by an essential gene.

机译：酵母mRNA帽甲基转移酶是一种50千达尔顿的蛋白质，由必不可少的基因编码。

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RNA (guanine-7-)methyltransferase, the enzyme responsible for methylating the 5' cap structure of eukaryotic mRNA, was isolated from extracts of Saccharomyces cerevisiae. The yeast enzyme catalyzed methyl group transfer from S-adenosyl-L-methionine to the guanosine base of capped, unmethylated poly(A). Cap methylation was stimulated by low concentrations of salt and was inhibited by S-adenosyl-L-homocysteine, a presumptive product of the reaction, but not by S-adenosyl-D-homocysteine. The methyltransferase sedimented in a glycerol gradient as a single discrete component of 3.2S. A likely candidate for the gene encoding yeast cap methyltransferase was singled out on phylogenetic grounds. The ABD1 gene, located on yeast chromosome II, encodes a 436-amino-acid (50-kDa) polypeptide that displays regional similarity to the catalytic domain of the vaccinia virus cap methyltransferase. That the ABD1 gene product is indeed RNA (guanine-7-)methyltransferase was established by expressing the ABD1 protein in bacteria, purifying the protein to homogeneity, and characterizing the cap methyltransferase activity intrinsic to recombinant ABD1. The physical and biochemical properties of recombinant ABD1 methyltransferase were indistinguishable from those of the cap methyltransferase isolated and partially purified from whole-cell yeast extracts. Our finding that the ABD1 gene is required for yeast growth provides the first genetic evidence that a cap methyltransferase (and, by inference, the cap methyl group) plays an essential role in cellular function in vivo.
机译：从酿酒酵母提取物中分离出RNA（鸟嘌呤7-）甲基转移酶，该酶负责使真核mRNA的5'帽结构甲基化。酵母酶催化甲基从S-腺苷-L-蛋氨酸转移到封端的未甲基化poly（A）的鸟嘌呤碱基上。低浓度的盐刺激了帽的甲基化，并被反应的推定产物S-腺苷-L-高半胱氨酸抑制，但未被S-腺苷-D-高半胱氨酸抑制。甲基转移酶以3.2S的单个离散成分的形式在甘油梯度中沉淀。从系统发育的角度出发，可能选择出编码酵母帽甲基转移酶的基因。位于酵母染色体II上的ABD1基因编码一个436个氨基酸（50 kDa）的多肽，该多肽与牛痘病毒帽甲基转移酶的催化结构域表现出区域相似性。通过在细菌中表达ABD1蛋白，纯化该蛋白至均质并表征重组ABD1固有的帽甲基转移酶活性，可以确定ABD1基因产物确实是RNA（鸟嘌呤7-）甲基转移酶。重组ABD1甲基转移酶的物理和生化特性与从全细胞酵母提取物中分离并部分纯化的帽甲基转移酶没有区别。我们发现ABD1基因是酵母生长所必需的，这提供了第一个遗传证据，即帽甲基转移酶（以及据推断帽甲基）在体内细胞功能中起着重要作用。

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