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首页> 外文期刊>Molecular and Cellular Biology >Trypanosome Capping Enzymes Display a Novel Two-Domain Structure
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Trypanosome Capping Enzymes Display a Novel Two-Domain Structure

机译：锥虫封顶酶显示新颖的两域结构

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The ubiquitous m7G cap of eukaryotic mRNAs and of precursors to the spliceosomal small nuclear RNAs (snRNAs) is the result of an essential RNA modification acquired during transcript elongation. In trypanosomes, the m7G cap is restricted to the spliced leader (SL) RNA and the precursors of U2, U3, and U4 snRNAs. mRNA capping in these organisms occurs posttranscriptionally bytrans splicing, which transfers the capped SL sequence to the 5′ ends of all mRNAs. The SL cap is the most elaborate cap structure known in nature and has been shown to consist of an m7G residue followed by four methylated nucleotides. UsingCrithidia fasciculata, we have characterized and purified the guanylyltransferase (capping enzyme), which transfers GMP from GTP to the diphosphate end of RNA. The corresponding gene codes for a protein of 697 amino acids, with the carboxy-terminal half of theC. fasciculata guanylyltransferase containing the six signature motifs previously identified in yeast capping enzymes. The amino-terminal half contains a domain that displays no resemblance to any other domain associated with capping enzymes. Intriguingly, this region harbors a consensus sequence for a phosphate-binding loop which is found in ATP- and GTP-binding proteins. This two-domain structure is also present in the Trypanosoma brucei capping enzyme, which shows 44% overall identity with the C. fasciculatacapping enzyme. Thus, this structure appears to be common to all trypanosomatid protozoa and defines a novel class of capping enzymes.
机译：真核mRNA和剪接小核RNA（snRNA）的前体普遍存在的m 7 G帽是转录本延伸过程中必需的RNA修饰的结果。在锥虫中，m 7 G帽仅限于剪接的前导（SL）RNA和U2，U3和U4 snRNA的前体。这些生物中的mRNA封端是通过 trans 剪接在转录后进行的，该操作将封端的SL序列转移到所有mRNA的5'末端。 SL帽是自然界中最复杂的帽结构，已显示它由一个m 7 G残基和四个甲基化核苷酸组成。我们使用 Crithidia fasciculata 鉴定并纯化了鸟苷酸转移酶（封端酶），该酶将GMP从GTP转移到RNA的二磷酸端。相应的基因编码具有697个氨基酸的蛋白质，其中C是羧基末端的一半。 fasciculata 鸟嘌呤基转移酶含有以前在酵母加帽酶中鉴定出的六个特征性基序。氨基末端的一半包含一个域，该域与与封端酶相关的任何其他域均不相似。有趣的是，该区域具有一个在ATP和GTP结合蛋白中发现的磷酸结合环的共有序列。在布鲁氏锥虫封端酶中也存在这种两个结构域的结构，该结构显示与 C的整体同一性为44％。 fasciculata 封端酶。因此，这种结构似乎对所有锥虫原虫都是共有的，并定义了一类新型的加帽酶。

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