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Transfer RNA (tRNA) is produced as a precursor molecule that needs to be processed at its 3' and 5' ends. Ribonuclease P is the sole endonuclease responsible for processing the 5' end of tRNA by cleaving the precursor and leading to tRNA maturation. It was one of the first catalytic RNA molecules identified and consists of a single RNA component in all organisms and only one protein component in bacteria. It is a true multi-turnover ribozyme and one of only two ribozymes (the other being the ribosome) that are conserved in all kingdoms of life. Here we show the crystal structure at 3.85 A resolution of the RNA component of Thermotoga maritima ribonuclease P. The entire RNA catalytic component is revealed, as well as the arrangement of the two structural domains. The structure shows the general architecture of the RNA molecule, the inter- and intra-domain interactions, the location of the universally conserved regions, the regions involved in pre-tRNA recognition and the location of the active site. A model with bound tRNA is in agreement with all existing data and suggests the general basis for RNA-RNA recognition by this ribozyme. 相似文献
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Role for a bidentate ribonuclease in the initiation step of RNA interference 总被引:344,自引:0,他引:344
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Changes to the conformation of coding and non-coding RNAs form the basis of elements of genetic regulation and provide an important source of complexity, which drives many of the fundamental processes of life. Although the structure of RNA is highly flexible, the underlying dynamics of RNA are robust and are limited to transitions between the few conformations that preserve favourable base-pairing and stacking interactions. The mechanisms by which cellular processes harness the intrinsic dynamic behaviour of RNA and use it within functionally productive pathways are complex. The versatile functions and ease by which it is integrated into a wide variety of genetic circuits and biochemical pathways suggests there is a general and fundamental role for RNA dynamics in cellular processes. 相似文献
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FENG Juan LI XueFeng&LIU Yuan School of Life Science Technology University of Electronic Science&Technology of China Chengdu China 《科学通报(英文版)》2007,(8)
Steady-state absorption spectroscopy,circular dichroism,and resonance Raman spectroscopy have been used to investigate the thermal stability of LH2 complex isolated from purple photosynthetic bacterium Rps.palustris.The results show that:1)upon increasing the temperature,a transition from B800 and B850 to free bacteriochlorophyll(B780)happens;2)a gradual decrease and disappearance of CD signal in visible region occur;3)a shift of the frequency,belonging to C==C and C—C stretching vibration,to higher wavenumber takes place.It is suggested that LH2 complex can be dissociated in the presence of B800,B850 and carotenoids simultaneously.Single-exponential fitting on the dynamic decay curves gives the apparent time constants of hundreds of minutes for various pigments. 相似文献
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Ribonuclease (RNase) P is the universal ribozyme responsible for 5'-end tRNA processing. We report the crystal structure of the Thermotoga maritima RNase P holoenzyme in complex with tRNA(Phe). The 154?kDa complex consists of a large catalytic RNA (P RNA), a small protein cofactor and a mature tRNA. The structure shows that RNA-RNA recognition occurs through shape complementarity, specific intermolecular contacts and base-pairing interactions. Soaks with a pre-tRNA 5' leader sequence with and without metal help to identify the 5' substrate path and potential catalytic metal ions. The protein binds on top of a universally conserved structural module in P RNA and interacts with the leader, but not with the mature tRNA. The active site is composed of phosphate backbone moieties, a universally conserved uridine nucleobase, and at least two catalytically important metal ions. The active site structure and conserved RNase P-tRNA contacts suggest a universal mechanism of catalysis by RNase P. 相似文献
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聚乙烯胺Hofmann降级法合成及其热稳定性研究 总被引:6,自引:0,他引:6
研究了聚丙烯酰胺(PAA)的Hofmann降级重排反应,并对不同胺化度的聚乙烯胺盐酸盐(PVAmHCl)进行了热重分析,结果表明:聚丙烯酰胺质量分数小于5%时,产品胺化度随着质量分数的增大而增加,而当大于5%时,胺化度随着其质量分数的增大有所降低;当n(NaOCl):n(paa)=1,n(NaOH)/n(PAA)=1(第一步),n(NaOH)/n(PAA)=30(第二步),反应时间为10h时,产物的胺化度相应达到最大值,热失重分析结果表明,随着产品胺化度的提高,产品的初始热失重温度有所降低,而且出现两个主要的失重区,这说明部分胺化的聚乙烯胺盐酸盐的热稳定性比聚丙烯酰胺的有所降低。 相似文献
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建立苯酚及其降解产物(邻苯二酚,间苯二酚,对苯醌)的高效液相色谱分析方法,用甲醇:水为50:50作流动相,在25℃以0.5ml/min的流速进样分析.线性范围为2-10mg/L,采用外标法定量,苯酚及其降解物的相对标准偏差和回收率分别为0.4%.1.6%和95.3%.101.6%,检出限为0.0735-0.1298mg/L.该方法准确,高效,适用于苯酚及其降解产物的分离测定. 相似文献
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Recently, substantial advances in the understanding of the molecular pathogenesis of inflammatory bowel disease (IBD) have been made owing to three related lines of investigation. First, IBD has been found to be the most tractable of complex disorders for discovering susceptibility genes, and these have shown the importance of epithelial barrier function, and innate and adaptive immunity in disease pathogenesis. Second, efforts directed towards the identification of environmental factors implicate commensal bacteria (or their products), rather than conventional pathogens, as drivers of dysregulated immunity and IBD. Third, murine models, which exhibit many of the features of ulcerative colitis and seem to be bacteria-driven, have helped unravel the pathogenesis/mucosal immunopathology of IBD. 相似文献
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Formation of a nine-subunit complex by HLA class II glycoproteins and the invariant chain 总被引:12,自引:0,他引:12
HLA class II molecules are heterodimeric transmembrane glycoproteins that bind and present processed antigenic peptides to CD4-positive T lymphocytes. Intracellularly, class II molecules associate with a third subunit termed the invariant (I) chain. Here we describe the physical characteristics of the intracellular class II alpha beta I complex. Chemical crosslinking, size exclusion chromatography and sedimentation velocity studies demonstrate that the alpha beta I complex is a nine-subunit transmembrane protein that contains three alpha beta dimers associated with an I chain trimer. The organization of class II alpha- and beta-subunits in such a multimer may have a role in the documented ability of the I chain to inhibit peptide binding to class II molecules. In addition, the formation of the nine-chain complex may induce the structural changes necessary to overcome the cytoplasmic retention signal responsible for the localization of free I chain in the endoplasmic reticulum, releasing class II-I chain complexes for transport to endosomes. 相似文献
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鲨软骨碱降解动力学及微观结构分析 总被引:3,自引:0,他引:3
对鲨软骨的碱降解动力学及其微观结构变化进行了较深入的研究,实验发现,鲨碱降解过程基本符合“碱-底物复合物”机理。电子显微结构分析表明,鲨软骨的降解通过“表面-孔穴”方式进行的。 相似文献
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Cdc20 and Cdh1 are the activating subunits of the anaphase-promoting complex (APC), an E3 ubiquitin ligase that drives cells into anaphase by inducing degradation of cyclin B and the anaphase inhibitor securin. To prevent chromosome missegregation, APC activity directed against these mitotic regulators must be inhibited until all chromosomes are properly attached to the mitotic spindle. Here we show that in mitosis timely destruction of securin by APC is regulated by the nucleocytoplasmic transport factors Rae1 and Nup98. We show that combined Rae1 and Nup98 haploinsufficiency in mice results in premature separation of sister chromatids, severe aneuploidy and untimely degradation of securin. We find that Rae1 and Nup98 form a complex with Cdh1-activated APC (APC(Cdh1)) in early mitosis and specifically inhibit APC(Cdh1)-mediated ubiquitination of securin. Dissociation of Rae1 and Nup98 from APC(Cdh1) coincides with the release of the mitotic checkpoint protein BubR1 from Cdc20-activated APC (APC(Cdc20)) at the metaphase to anaphase transition. Together, our results suggest that Rae1 and Nup98 are temporal regulators of APC(Cdh1) that maintain euploidy by preventing unscheduled degradation of securin. 相似文献
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水中藻毒素降解的影响因素及其净水工艺控制 总被引:4,自引:0,他引:4
藻毒素污染已成为普遍关注的水质问题,在水环境中,藻毒素的迁移转化受光照、温度、有机物、溶解氧、水生生物等因素的共同影响。单元净水工艺(混凝、沉淀、砂滤、氯化等)和常规组合工艺对藻毒素的去除率较低,常规工艺+活性炭过滤、臭氧+常规工艺的去除率可达100%,不破坏藻细胞而能够大量降低其数量的预处理+臭氧+常规工艺+ 性炭工艺应能够取得最佳的解毒效果。 相似文献
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Direction of in vivo degradation of a messenger RNA 总被引:2,自引:0,他引:2
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A Rad26-Def1 complex coordinates repair and RNA pol II proteolysis in response to DNA damage 总被引:11,自引:0,他引:11
Woudstra EC Gilbert C Fellows J Jansen L Brouwer J Erdjument-Bromage H Tempst P Svejstrup JQ 《Nature》2002,415(6874):929-933
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复杂物系的介观结构和DPD模拟 总被引:2,自引:0,他引:2
耗散粒子动力学(DPD)模拟方法是研究复杂物系介观结构的一种重要手段。首先简要介绍了DPD模拟方法。然后介绍了实际物系与DPD模型映射的2种方法,即Groot和Warren方法以及Pagonabarraga和Frenkel方法。最后对DPD模拟的理论和应用研究进展作了回顾。 相似文献
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Unravelling angiosperm genome evolution by phylogenetic analysis of chromosomal duplication events 总被引:38,自引:0,他引:38
Conservation of gene order in vertebrates is evident after hundreds of millions of years of divergence, but comparisons of the Arabidopsis thaliana sequence to partial gene orders of other angiosperms (flowering plants) sharing common ancestry approximately 170-235 million years ago yield conflicting results. This difference may be largely due to the propensity of angiosperms to undergo chromosomal duplication ('polyploidization') and subsequent gene loss ('diploidization'); these evolutionary mechanisms have profound consequences for comparative biology. Here we integrate a phylogenetic approach (relating chromosomal duplications to the tree of life) with a genomic approach (mitigating information lost to diploidization) to show that a genome-wide duplication post-dates the divergence of Arabidopsis from most dicots. We also show that an inferred ancestral gene order for Arabidopsis reveals more synteny with other dicots (exemplified by cotton), and that additional, more ancient duplication events affect more distant taxonomic comparisons. By using partial sequence data for many diverse taxa to better relate the evolutionary history of completely sequenced genomes to the tree of life, we foster comparative approaches to the study of genome organization, consequences of polyploidy, and the molecular basis of quantitative traits. 相似文献