IDENTIFICATION OF A NOVEL TRANSLATION FACTOR NECESSARY FOR THE INCORPORATION OF SELENOCYSTEINE INTO PROTEIN
IDENTIFICATION OF A NOVEL TRANSLATION FACTOR NECESSARY FOR THE INCORPORATION OF SELENOCYSTEINE INTO PROTEIN
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DOI：
10.1038/342453a0
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发表时间：
1989-11-23
期刊：
影响因子：
64.8
通讯作者：
BOCK, A
中科院分区：
文献类型：
--
作者：
FORCHHAMMER, K;LEINFELDER, W;BOCK, A
在原核生物和真核生物中硒蛋白的生物合成过程中，硒代半胱氨酸通过由通常充当终止密码子 3-5 的 UGA 密码子指导的过程共翻译并入新生多肽链 1, 2 中。最近，已鉴定出四个基因，其产物是大肠杆菌6中硒代半胱氨酸掺入所必需的。其中一个基因 selC 编码一种新的转移 RNA 种类 (tRNAUCA)，它接受丝氨酸并通过识别特定的 UGA 密码子 7 来共翻译插入硒代半胱氨酸。附着在该 tRNA 上的丝氨酸残基在依赖于功能性 selA 和 selD 基因产物的反应中转化为硒代半胱氨酸8。相比之下，这些selB基因产物（SELB）直到硒代半胱氨酰-tRNA生物合成之后才需要。在这里，我们提供的证据表明 SELB 是一种新颖的翻译因子。 SELB 的推导氨基酸序列与翻译起始因子-2 (IF-2) 和延伸因子 Tu (EF-Tu) 的序列表现出广泛的同源性。此外，纯化的 SELB 蛋白以 1:1 摩尔比结合鸟嘌呤核苷酸，并特异性地复合硒代半胱氨酰-tRNAUCA，但不与丝氨酰-tRNAUCA 相互作用。因此，SELB 可能是一种氨基酸特异性延伸因子，在特殊的翻译步骤中取代 EF-Tu。
DURING the biosynthesis of selenoproteins in both prokaryotes and eukaryotes, selenocysteine is cotranslationally incorporated into the nascent polypeptide chain1, 2through a process directed by a UGA codon that normally functions as a stop codon3–5. Recently, four genes have been identified whose products are required for selenocysteine incorporation inEscherichia coli6. One of these genes,selC, codes for a novel transfer RNA species (tRNAUCA) that accepts serine and cotranslationally inserts selenocysteine by recognizing the specific UGA codon7. The serine residue attached to this tRNA is converted to selenocysteine in a reaction dependent on functionalselAandselDgene products8. By contrast, theselBgene product (SELB) is not required until after selenocysteyl-tRNA biosynthesis8. Here we present evidence indicating that SELB is a novel translation factor. The deduced amino-acid sequence of SELB exhibits extensive homology with the sequences of the translation initiation factor-2 (IF-2) and elongation factor Tu (EF-Tu). Furthermore, purified SELB protein binds guanine nucleotides in a 1:1 molar ratio and specifically complexes selenocysteyl-tRNAUCA, but does not interact with seryl-tRNAUCA. Thus, SELB could be an amino acid-specific elongation factor, replacing EF-Tu in a special translational step.