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Primary structure of human nuclear ribonucleoprotein particle C proteins: conservation of sequence and domain structures in heterogeneous nuclear RNA mRNA and pre-rRNA-binding proteins.

机译:人核核糖核蛋白颗粒C蛋白的一级结构:异质核RNAmRNA和前rRNA结合蛋白中序列和结构域结构的保守性。

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摘要

In the eucaryotic nucleus, heterogeneous nuclear RNAs exist in a complex with a specific set of proteins to form heterogeneous nuclear ribonucleoprotein particles (hnRNPs). The C proteins, C1 and C2, are major constituents of hnRNPs and appear to play a role in RNA splicing as suggested by antibody inhibition and immunodepletion experiments. With the use of a previously described partial cDNA clone as a hybridization probe, full-length cDNAs for the human C proteins were isolated. All of the cDNAs isolated hybridized to two poly(A)+ RNAs of 1.9 and 1.4 kilobases (kb). DNA sequencing of a cDNA clone for the 1.9-kb mRNA (pHC12) revealed a single open reading frame of 290 amino acids coding for a protein of 31,931 daltons and two polyadenylation signals, AAUAAA, approximately 400 base pairs apart in the 3' untranslated region of the mRNA. DNA sequencing of a clone corresponding to the 1.4-kb mRNA (pHC5) indicated that the sequence of this mRNA is identical to that of the 1.9-kb mRNA up to the first polyadenylation signal which it uses. Both mRNAs therefore have the same coding capacity and are probably transcribed from a single gene. Translation in vitro of the 1.9-kb mRNA selected by hybridization with a 3'-end subfragment of pHC12 demonstrated that it by itself can direct the synthesis of both C1 and C2. The difference between the C1 and C2 proteins which results in their electrophoretic separation is not known, but most likely one of them is generated from the other posttranslationally. Since several hnRNP proteins appeared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis as multiple antigenically related polypeptides, this raises the possibility that some of these other groups of hnRNP proteins are also each produced from a single mRNA. The predicted amino acid sequence of the protein indicates that it is composed of two distinct domains: an amino terminus that contains what we have recently described as a RNP consensus sequence, which is the putative RNA-binding site, and a carboxy terminus that is very negatively charged, contains no aromatic amino acids or prolines, and contains a putative nucleoside triphosphate-binding fold, as well as a phosphorylation site for casein kinase type II. The RNP consensus sequence was also found in the yeast poly(A)-binding protein (PABP), the heterogeneous nuclear RNA-binding proteins A1 and A2, and the pre-rRNA binding protein C23. All of these proteins are also composed of at least two distinct domains: an amino terminus, which possesses one or more RNP consensus sequences, and a carboxy terminus, which is unique to each protein, being very acidic in the C proteins and rich in glycine in A1, and C23 and rich in proline in the poly(A)-binding protein. These findings suggest that the amino terminus of these proteins possesses a highly conserved RNA-binding domain, whereas the carboxy terminus contains a region essential to the unique function and interactions of each of the RNA-binding proteins.
机译:在真核中,异质核RNA与一组特定的蛋白质复合存在,形成异质核核糖蛋白颗粒(hnRNPs)。 C蛋白C1和C2是hnRNP的主要组成部分,似乎在RNA剪接中发挥作用,如抗体抑制和免疫耗竭实验所暗示的那样。使用先前描述的部分cDNA克隆作为杂交探针,分离了人C蛋白的全长cDNA。分离出的所有cDNA与1.9和1.4千碱基(kb)的两个poly(A)+ RNA杂交。对1.9-kb mRNA(pHC12)的cDNA克隆进行的DNA测序显示,共有290个氨基酸的单一开放阅读框,编码31,931道尔顿的蛋白质和两个多腺苷酸化信号AAUAAA,在3'非翻译区相距约400个碱基对mRNA。对应于1.4 kb mRNA(pHC5)的克隆的DNA测序表明,直到使用的第一个多聚腺苷酸信号为止,该mRNA的序列与1.9 kb mRNA的序列相同。因此,两个mRNA具有相同的编码能力,并且很可能是从单个基因转录而来的。通过与pHC12的3'末端亚片段杂交选择的1.9-kb mRNA的体外翻译表明,它本身可以指导C1和C2的合成。 C1和C2蛋白之间导致电泳分离的差异是未知的,但是很可能其中一个是从另一个翻译后产生的。由于十二烷基硫酸钠-聚丙烯酰胺凝胶电泳显示了多个hnRNP蛋白,它们是多个抗原相关多肽,因此增加了一些其他组的hnRNP蛋白也分别由单个mRNA产生的可能性。蛋白质的预测氨基酸序列表明它由两个不同的结构域组成:一个氨基末端包含一个我们最近描述的RNP共有序列,它是推定的RNA结合位点,另一个羧基末端是带负电荷,不包含芳香族氨基酸或脯氨酸,并且包含推定的核苷三磷酸结合折叠以及II型酪蛋白激酶的磷酸化位点。在酵母聚(A)结合蛋白(PABP),异质核RNA结合蛋白A1和A2以及前rRNA结合蛋白C23中也发现了RNP共有序列。所有这些蛋白质还由至少两个不同的域组成:一个具有一个或多个RNP共有序列的氨基末端,和一个对每种蛋白质来说都是唯一的羧基末端,在C蛋白中呈酸性,富含甘氨酸在A1和C23中,富含脯氨酸的poly(A)结合蛋白。这些发现表明,这些蛋白质的氨基末端具有高度保守的RNA结合结构域,而羧基末端含有对于每种RNA结合蛋白质的独特功能和相互作用必不可少的区域。

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