真核mRNA3′非翻译区的功能研究进展

真核ｍＲＮＡ的３′非翻译区的功能比人们目前认为的更为复杂。近年来的研究揭示,ｍＲＮＡ３′非翻译区不但决定该ｍＲＮＡ的稳定性,而且还控制着该特定ｍＲＮＡ的翻译时间、翻译地点和翻译产物。值得注意的是真核ｍＲＮＡ３′非翻译区内的突变可能导致肿瘤的发生。文章介绍了１９９１—１９９２年间国际上关于３′非翻译区的一些新发现。     

真核生物mRNA 3′非翻译区的功能

真核生物mRNA的3′非翻译区的功能复杂多样,不仅能调控其mRNA的稳定性、控制mRNA的亚细胞定位,而且还在特定氨基酸的编码过程中起着指导作用.一些真核生物mRNA的3′非翻译区内的突变可引起疾病的发生.近几年的研究又发现,一些真核生物mRNA的3′非翻译区还具有抑制肿瘤生长的功能.     

真核mRNA 3′非翻译区在基因表达中的作用

真核生物mRNA的3′非翻译区(3′-UTR)在基因表达调控中发挥重要作用.它不仅调控mRNA在体内的稳定性和降解速率,控制着mRNA的利用效率,还参与mRNA翻译过程的调控.     

真核mRNA的3′非翻译区转录后水平调控作用研究进展

真核生物mRNA的3′非翻译区(3′-UTR)在基因表达的转录后调控中起着重要作用:3′-UTR内存在末端加工信号以指导mRNA3′末端的加工;3′-UTR不但控制mRNA的稳定性及降解速率、协助辨认特殊密码子,而且还控制着mRNA的翻译时间、位点及控制其翻译起始及效率等。     

真核mRNA的3′非翻译区转录后水平调控作用研究进展

真核生物mRNA的3′非翻译区(3′_UTR)在基因表达的转录后调控中起着重要作用:3′_UTR内存在末端加工信号以指导mRNA3′末端的加工;3′_UTR不但控制mRNA的稳定性及降解速率、协助辨认特殊密码子,而且还控制着mRNA的翻译时间、位点及控制其翻译起始及效率等。     

PI3KγmRNA 3′非翻译区可能存在基因表达负调控区

为探索人磷脂酰肌醇 3 激酶γ(phosphoinositide 3 kinasePI3Kγ)基因 3′端非翻译区内AU富含区是否在基因表达调控中起作用 ,首先通过生物信息学分析发现在其 3′端非翻译区 (UTR)内存在0 9kb的AU富含区 ,其中包括 4个AU富含元件 ,以及 1个与众多基因非翻译区高度同源的长 130个碱基的区域 .将AU富含区插入报告基因egfp的下游构建pcDNA3 egfp AUR表达载体 .将表达载体转导NIH 3T3,74 0 2及K5 6 2细胞 ,流式细胞检测egfp的表达情况 .PI3Kγ基因 3′非翻译区AU富含区可显著降低egfp的表达 2～ 3倍 (P <0 0 1) .利用放线菌素D阻断RNA转录后 ,Northern印迹分析结果显示egfp AURmRNA较egfpmRNA不稳定 .实验结果提示 ,PI3Kγ基因 3′非翻译区AU富含区内可能存在转录后水平的基因表达负调控区 ,该负调控区可在一定程度上加速mRNA的衰变     

PI3KγmRNA 3′非翻译区可能存在基因表达负调控区

为探索人磷脂酰肌醇 3 激酶γ(phosphoinositide 3 kinasePI3Kγ)基因 3′端非翻译区内AU富含区是否在基因表达调控中起作用 ,首先通过生物信息学分析发现在其 3′端非翻译区 (UTR)内存在0 9kb的AU富含区 ,其中包括 4个AU富含元件 ,以及 1个与众多基因非翻译区高度同源的长 130个碱基的区域 .将AU富含区插入报告基因egfp的下游构建pcDNA3 egfp AUR表达载体 .将表达载体转导NIH 3T3,74 0 2及K5 6 2细胞 ,流式细胞检测egfp的表达情况 .PI3Kγ基因 3′非翻译区AU富含区可显著降低egfp的表达 2～ 3倍 (P <0 0 1) .利用放线菌素D阻断RNA转录后 ,Northern印迹分析结果显示egfp AURmRNA较egfpmRNA不稳定 .实验结果提示 ,PI3Kγ基因 3′非翻译区AU富含区内可能存在转录后水平的基因表达负调控区 ,该负调控区可在一定程度上加速mRNA的衰变     

依赖于5′端非编码区高级结构的真核生物mRNA翻译调控

翻译水平的调控是真核基因表达调控的重要环节.近年来的研究表明,许多真核基因的翻译依赖于RNA 5′端非编码区的结构元件.一些小结构元件,如铁离子反应元件,具有1个茎环结构,由铁离子介导控制转铁蛋白的翻译. 核糖开关通过结合特定代谢分子在2种结构状态下切换,调控可变剪接和翻译起始.另1个高度结构化的mRNA元件是内部核糖体进入位点,通过富集核糖体和起始因子促进基因的表达.本文综述了依赖于小结构元件、内部核糖体进入位点和核糖开关的真核基因翻译起始调控相应的研究成果和研究方法.对于研究的前景以及可能存在的挑战也作出阐述.     

依赖于5′端非编码区高级结构的真核生物mRNA翻译调控

翻译水平的调控是真核基因表达调控的重要环节.近年来的研究表明,许多真核基因的翻译依赖于RNA5′端非编码区的结构元件.一些小结构元件,如铁离子反应元件,具有1个茎环结构,由铁离子介导控制转铁蛋白的翻译.核糖开关通过结合特定代谢分子在2种结构状态下切换,调控可变剪接和翻译起始.另1个高度结构化的mRNA元件是内部核糖体进入位点,通过富集核糖体和起始因子促进基因的表达.本文综述了依赖于小结构元件、内部核糖体进入位点和核糖开关的真核基因翻译起始调控相应的研究成果和研究方法.对于研究的前景以及可能存在的挑战也作出阐述.     

哺乳动物信使核糖核酸的结构与功能

信使核糖核酸(mRNA)的结构与功能是当代分子生物学的重要论题之一。近年哺乳动物 mRNA 结构与功能的研究进展颇为迅速,分离提纯的哺乳动物mRNA 的品种已日益增多,个别 mRNA 的核苷酸序列已基本搞清。哺乳动物 mRNA与其它真核生物,mRNA 相似,除含有为蛋白质的氨基酸序列编码的翻译部分外,还存在着包括“帽”、5′非翻译区,3′非翻译区与“尾”在内的非翻译部分。本文对哺乳动物 mRNA 上述区段的结构与功能分别作了介绍。同时,对此类 mRNA 在细胞内的分布、存在形式等也给予适当的介绍。     

Sequence conservation in the 3'-untranslated regions of neurone-specific enolase, lymphokine and protooncogene mRNAs

The C-terminal protein-coding and the entire 3'-untranslated regions of a cDNA corresponding to human neurone-specific enolase mRNA have been sequenced. The 3'-untranslated region is 892 bases long and shows a high degree of homology with the 3'-untranslated region of rat neurone-specific enolase mRNA. This sequence conservation is not seen in non-neuronal enolase mRNAs. Features of the conserved sequence include an A-rich region approx. 250 bases from the stop codon at a point corresponding to the polyadenylation signal site in non-neuronal enolase mRNA, and a repeating ATTT sequence. This unusual motif in eukaryotic mRNAs has previously been reported in the 3'-untranslated regions of lymphokine and protooncogene mRNAs.     

Translation efficiency of zein mRNA is reduced by hybrid formation between the 5'- and 3'-untranslated region

The secondary structure of zein mRNA affects its translation potential. Here we show that in a cell-free system the translation efficiency of zein mRNA containing inverted repeats in the 5'- and 3'-untranslated regions is reduced. This translational block is released after deletion of the 3'-inverted repeat. We conclude that the translational block is caused by hybrid formation between the two inverted repeats. The translational efficiency of zein mRNAs, is also affected by varying the length or the primary structure of the 5'-untranslated region.     

Cloning, sequencing, and characterization of alternatively spliced glutaredoxin 1 cDNA and its genomic gene: chromosomal localization, mrna stability, and origin of pseudogenes

Alternatively spliced human glutaredoxin (Grx1(as)) cDNA was isolated from a neutrophil cDNA library, using a (32)P-labeled human glutaredoxin (Grx1) cDNA probe under non-stringent conditions. The sequence of Grx1(as) cDNA indicated that the open reading frame of the gene was identical to the open reading frame of the previously reported first human glutaredoxin (Grx1) cDNA, but the 3'-untranslated region of Grx1(as) was not homologous to Grx1 cDNA. Northern blot and RT-PCR analyses showed Grx1(as) mRNA was expressed in normal human neutrophils and transformed cells including U937, HL-60, THP, and Jurkat cells. Cloning and sequencing of the genomic gene corresponding to Grx1(as) cDNA showed that two different glutaredoxin cDNAs (Grx1(as) and Grx1) were generated from the same genomic gene via alternative splicing. Origination of Grx1(as) and Grx1 from the same gene was confirmed by chromosomal localization of the Grx1(as) gene to chromosome 5q13, the same location where the Grx1 gene was localized previously. During screening of the Grx1(as) genomic gene, two additional glutaredoxin pseudogenes were also isolated. Surprisingly, these pseudogenes contained 3'-untranslated regions that were nearly identical to the 3'-untranslated regions of Grx1(as,) not Grx1, cDNA. Because 3'-untranslated regions may be important in stabilizing mRNAs, the effect of the two 3'-untranslated regions of Grx1 and Grx1(as) on mRNA stability was investigated using luciferase reporter vectors with the 3'-untranslated regions. Luciferase activity was 2.6-fold greater in cells transfected with the reporter vector containing the 3'-untranslated region of Grx1(as) cDNA compared with the 3'-untranslated region of Grx1 cDNA. These data indicate that Grx1(as) cDNA is an alternatively spliced human Grx1 cDNA and that the Grx1(as) 3'-untranslated region may have a role in stabilizing mRNA.     

Nucleotide sequence of a cDNA for the common alpha subunit of the bovine pituitary glycoprotein hormones. Conservation of nucleotides in the 3'-untranslated region of bovine and human pre-alpha subunit mRNAs

A cDNA clone for the pre-alpha subunit of the pituitary glycoprotein hormones has been isolated from a bovine pituitary cDNA library through the use of a pool of synthetic oligodeoxynucleotide probes. This clone, designated pB alpha, contains a 564-base pair insert which includes a portion of the signal sequence, the entire coding sequence of the mature protein, and 224 base pairs of the 3'-untranslated sequence. As expected, the nucleotide and amino acid sequence of the mature bovine alpha subunit was homologous to the sequences reported for humans and rodents, with the most extensive homology occurring between bovine and rodents (85-90%). However, a comparison of the 3'-untranslated regions of pre-alpha subunit mRNA from three different mammalian species indicated that in bovine and rat, or in human and rat, these sequences have rapidly diverged, yielding respective homologies of 21 and 36%. In contrast, the sequence homology observed between the 3'-untranslated regions of bovine and human was 79%, which approaches the level of homology shared by their coding sequences. Thus, the conservation of the 3'-untranslated sequence in bovine and human pre-alpha subunit mRNA may be an indication that this region is functionally significant in these two species.     

Rainbow trout has two genes for growth hormone

We report the primary structures of two mRNA species (GH1 and GH2), each predicted from the cloned cDNA and genomic gene sequences, that encode growth hormone in rainbow trout (Salmo gairdneri). Both GH1 and GH2 mRNA contain open reading frames comprising 630 nucleotides and encode 210 amino acid residues, of which 11 are variant. The translated regions of mRNA are flanked by a short 5'-untranslated sequence, which is highly conserved, and a relatively long 3'-untranslated sequence, which is highly divergent. The differences at the 3'-untranslated regions suggest that the GH1 and GH2 mRNA originate from different loci. RNA blot analysis of trout pituitary RNA using an oligonucleotide probe specific for the GH2 sequence indicates that the cloned gene is expressed. The GH1 and GH2 mRNA likely are transcribed from two distinct loci, which were duplicated during tetraploidization of the salmonid genome between 50 and 100 million years ago.     

Annexin A2 recognises a specific region in the 3'-UTR of its cognate messenger RNA

Annexin A2 is a multifunctional Ca(2+)- and lipid-binding protein. We previously showed that a distinct pool of cellular Annexin A2 associates with mRNP complexes or polysomes associated with the cytoskeleton. Here we report in vitro and in vivo experiments showing that Annexin A2 present in this subset of mRNP complexes interacts with its cognate mRNA and c-myc mRNA, but not with beta(2)-microglobulin mRNA translated on membrane-bound polysomes. The protein recognises sequence elements within the untranslated regions, but not within the coding region, of its cognate mRNA. Alignment of the Annexin A2-binding 3'-untranslated regions of annexin A2 mRNA from several species reveals a five nucleotide consensus sequence 5'-AA(C/G)(A/U)G. The Annexin A2-interacting region of the 3'-untranslated region can be mapped to a sequence of about 100 nucleotides containing two repeats of the consensus sequence. The binding elements appear to involve both single and double stranded regions, indicating that a specific higher order mRNA structure is required for binding to Annexin A2. We suggest that this type of interaction is representative for a group of mRNAs translated on cytoskeleton-bound polysomes.     

Higher order structures of the 5'-proximal region decrease the efficiency of translation of the porcine pro-opiomelanocortin mRNA

The SP6 polymerase/promoter system was used to synthesize porcine pro-opiomelanocortin mRNAs with nucleotide sequence deletions in the 5'- as well as 3'-untranslated and coding regions. The translational efficiency of the mutant mRNAs was evaluated by cell-free translation or by monitoring the rate and extent of ribosome binding in the presence of sparsomycin. The results of these experiments indicate that specific nucleotide sequences in the 5'-untranslated and coding regions of the pro-opiomelanocortin mRNA decrease its rate of translation. Structure mapping of the mRNA with double-strand and single-strand specific nucleases suggests that these sequences can form stable secondary structures.