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Identification of a novel HIV-1 TAR RNA bulge binding protein.   总被引:6,自引:4,他引:2       下载免费PDF全文
The Tat protein binds to TAR RNA to stimulate the expression of the human immunodeficiency virus type 1 (HIV-1) genome. Tat is an 86 amino acid protein that contains a short region of basic residues (aa49-aa57) that are required for RNA binding and TAR is a 59 nucleotide stem-loop with a tripyrimidine bulge in the upper stem. TAR is located at the 5' end of all viral RNAs. In vitro, Tat specifically interacts with TAR by recognising the sequence of the bulge and upper stem, with no requirement for the loop. However, in vivo the loop sequence is critical for activation, implying a requirement for accessory cellular TAR RNA binding factors. A number of TAR binding cellular factors have been identified in cell extracts and various models for the function of these factors have been suggested, including roles as coactivators and inhibitors. We have now identified a novel 38 kD cellular factor that has little general, single-stranded or double-stranded RNA binding activity, but that specifically recognises the bulge and upper stem region of TAR. The protein, referred to as BBP (bulge binding protein), is conserved in mammalian and amphibian cells and in Schizosaccharomyces pombe but is not found in Saccharomyces cerevisiae. BBP is an effective competitive inhibitor of Tat binding to TAR in vitro. Our data suggest that the bulge-stem recognition motif in TAR is used to mediate cellular factor/RNA interactions and indicates that Tat action might be inhibited by such competing reactions in vivo.  相似文献   

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Translation of poliovirion RNA in HeLa S10 extracts resulted in the formation of RNA replication complexes which catalyzed the asymmetric replication of poliovirus RNA. Synthesis of poliovirus RNA was detected in unfractionated HeLa S10 translation reactions and in RNA replication complexes isolated from HeLa S10 translation reactions by pulse-labeling with [32P]CTP. The RNA replication complexes formed in vitro contained replicative-intermediate RNA and were enriched in viral protein 3CD and the membrane-associated viral proteins 2C, 2BC, and 3AB. Genome-length poliovirus RNA covalently linked to VPg was synthesized in large amounts by the replication complexes. RNA replication was highly asymmetric, with predominantly positive-polarity RNA products. Both anti-VPg antibody and guanidine HCl inhibited RNA replication and virus formation in the HeLa S10 translation reactions without affecting viral protein synthesis. The inhibition of RNA synthesis by guanidine was reversible. The reversible nature of guanidine inhibition was used to demonstrate the formation of preinitiation RNA replication complexes in reaction mixes containing 2 mM guanidine HCl. Preinitiation complexes sedimented upon centrifugation at 15,000 x g and initiated RNA replication upon their resuspension in reaction mixes lacking guanidine. Initiation of RNA synthesis by preinitiation complexes did not require active protein synthesis or the addition of soluble viral proteins. Initiation of RNA synthesis by preinitiation complexes, however, was absolutely dependent on soluble HeLa cytoplasmic factors. Preinitiation complexes also catalyzed the formation of infectious virus in reaction mixes containing exogenously added capsid proteins. The titer of infectious virus produced in such trans-encapsidation reactions reached 4 x 10(7) PFU/ml. The HeLa S10 translation-RNA replication reactions represent an efficient in vitro system for authentic poliovirus replication, including protein synthesis, polyprotein processing, RNA replication, and virus assembly.  相似文献   

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Pur alpha is an abundant protein in the brain and binds to a (GGN)n sequence, PUR element. It has been shown that Pur alpha not only interacts with single stranded DNA and RNA, but also with various proteins. In the present study, we tried to search for Pur alpha-binding proteins (PurBPs) in mouse brain by the overlay assay with GST-Pur alpha as a ligand. Three PurBPs of 35, 38 and 40 kDa were found mostly in the nuclear extract (N.Ext.) and they were not detected by the pretreatment of N.Ext. with trypsin, but not with RNase or DNase. The three PurBPs disappeared by the addition of ssCRE (single stranded cAMP response element) containing a PUR element, but not by DeltaGGN ssCRE (deletion of the PUR element from the ssCRE). The PurBPs were abundantly expressed in the brain as Pur alpha. We also determined a region in Pur alpha which is required for the association with the PurBPs by using deletion mutants of Pur alpha. These biochemical properties of the PurBPs are different from the reported nuclear Pur alpha-binding proteins such as Sp1 and pRb.  相似文献   

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Trans-activation by HIV-1 Tat via a heterologous RNA binding protein   总被引:57,自引:0,他引:57  
M J Selby  B M Peterlin 《Cell》1990,62(4):769-776
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反式激活应答(transactivation response,TAR)元件RNA作为HIV-1中的一种非编码RNA,从转录与翻译水平负调控HIV-1的基因表达.同时HIV-1采取了相应的策略拮抗TAR RNA的负调控作用:病毒蛋白Tat或细胞蛋白TAR RNA结合蛋白(TRBP)结合TAR RNA后,分别在转录与翻译水平促进HIV-1的基因表达.此外,TAR编码的miRNA有助于保持HIV的潜伏感染及阻止细胞凋亡.TAR与其它蛋白间相互作用及其功能的研究对于深入了解HIV-1感染细胞后的调控机制,寻求新的抗HIV治疗靶点具有重要意义.  相似文献   

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为了抑制Tat蛋白的反式激活作用,在细胞内大量表达外源TARRNA使其与Tat蛋白结合,从而竞争性抑制其与HIV-1LTR的TARRNA元件结合.构建了以HIV-1LTRYL158(-158~+180)为启动子,分别含有4,8和15个拷贝的TAR-CoreRNA诱饵(decoy)表达质粒;以荧光酶基因为报告基因,检测了瞬时共转染体系中含不同拷贝数的TAR-CoreDNA转录产物对Tat蛋白反式激活作用的影响.结果证明,TAR-CoreRNA诱饵对Tat蛋白活性具有很强的抑制作用,其抑制程度与TAR-CoreDNA串联体的拷贝数有关.  相似文献   

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HIV-1 Tat protein trans-activates transcription in vitro   总被引:55,自引:0,他引:55  
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