Crystal structure of the eukaryotic 40S ribosomal subunit in complex with initiation factor 1

Eukaryotic ribosomes are substantially larger and more complex than their bacterial counterparts. Although their core function is conserved, bacterial and eukaryotic protein synthesis differ considerably at the level of initiation. The eukaryotic small ribosomal subunit (40S) plays a central role in this process; it binds initiation factors that facilitate scanning of messenger RNAs and initiation of protein synthesis. We have determined the crystal structure of the Tetrahymena thermophila 40S ribosomal subunit in complex with eukaryotic initiation factor 1 (eIF1) at a resolution of 3.9 angstroms. The structure reveals the fold of the entire 18S ribosomal RNA and of all ribosomal proteins of the 40S subunit, and defines the interactions with eIF1. It provides insights into the eukaryotic-specific aspects of protein synthesis, including the function of eIF1 as well as signaling and regulation mediated by the ribosomal proteins RACK1 and rpS6e.     

Structure of the S15,S6,S18-rRNA complex: assembly of the 30S ribosome central domain

The crystal structure of a 70-kilodalton ribonucleoprotein complex from the central domain of the Thermus thermophilus 30S ribosomal subunit was solved at 2.6 angstrom resolution. The complex consists of a 104-nucleotide RNA fragment composed of two three-helix junctions that lie at the end of a central helix, and the ribosomal proteins S15, S6, and S18. S15 binds the ribosomal RNA early in the assembly of the 30S ribosomal subunit, stabilizing a conformational reorganization of the two three-helix junctions that creates the RNA fold necessary for subsequent binding of S6 and S18. The structure of the complex demonstrates the central role of S15-induced reorganization of central domain RNA for the subsequent steps of ribosome assembly.     

Hepatitis C virus IRES RNA-induced changes in the conformation of the 40s ribosomal subunit

Initiation of protein synthesis in eukaryotes requires recruitment of the 40S ribosomal subunit to the messenger RNA (mRNA). In most cases, this depends on recognition of a modified nucleotide cap on the 5' end of the mRNA. However, an alternate pathway uses a structured RNA element in the 5' untranslated region of the messenger or viral RNA called an internal ribosomal entry site (IRES). Here, we present a cryo-electron microscopy map of the hepatitis C virus (HCV) IRES bound to the 40S ribosomal subunit at about 20 A resolution. IRES binding induces a pronounced conformational change in the 40S subunit and closes the mRNA binding cleft, suggesting a mechanism for IRES-mediated positioning of mRNA in the ribosomal decoding center.     

Crystal structure of the eukaryotic 60S ribosomal subunit in complex with initiation factor 6

Protein synthesis in all organisms is catalyzed by ribosomes. In comparison to their prokaryotic counterparts, eukaryotic ribosomes are considerably larger and are subject to more complex regulation. The large ribosomal subunit (60S) catalyzes peptide bond formation and contains the nascent polypeptide exit tunnel. We present the structure of the 60S ribosomal subunit from Tetrahymena thermophila in complex with eukaryotic initiation factor 6 (eIF6), cocrystallized with the antibiotic cycloheximide (a eukaryotic-specific inhibitor of protein synthesis), at a resolution of 3.5 angstroms. The structure illustrates the complex functional architecture of the eukaryotic 60S subunit, which comprises an intricate network of interactions between eukaryotic-specific ribosomal protein features and RNA expansion segments. It reveals the roles of eukaryotic ribosomal protein elements in the stabilization of the active site and the extent of eukaryotic-specific differences in other functional regions of the subunit. Furthermore, it elucidates the molecular basis of the interaction with eIF6 and provides a structural framework for further studies of ribosome-associated diseases and the role of the 60S subunit in the initiation of protein synthesis.     

大熊猫核糖体蛋白S17亚基基因（rps17）的克隆及序列分析

RPS17蛋白是核糖体40S亚基的组成部分,由rps17基因编码.为了解大熊猫核糖体蛋白亚基rps17基因的结构特点及其与已报道的人和其他哺乳动物核糖体蛋白亚基rps17基因的异同,分别运用RT-PCR和PCR技术,从大熊猫肌肉组织的mRNA中成功克隆了核糖体蛋白亚基S17基因的cDNA序列以及从总DNA中成功克隆了S17基因的结构基因序列.序列分析发现,大熊猫核糖体蛋白亚基S17基因的表达序列长为457bp,开放阅读框(ORF)为408bp,编码135个氨基酸的蛋白质.结构基因序列长2 368bp,含有4个外显子和3个内含子.拓扑预测显示,核糖体蛋白亚基RPS17的相对分子质量为15.52×103,PI为10.26,含有5个类型的功能位点,即:5个蛋白激酶C磷酸化位点,1个酪蛋白激酶II磷酸化位点,1个酪氨酸激酶磷酸化位点,1个N-豆蔻酰化位点及1个核糖体蛋白S17Esignature位点.进一步分析发现,该基因的表达序列及其编码的氨基酸序列与已报道的部分哺乳动物有很高的相似性,其蛋白质的高级结构除褐家鼠外与其它物种也具有一致性.对大熊猫rps17基因及其表达的蛋白质结构的比较研究,旨在丰富和完善哺乳动物r...     

Erythromycin-resistant mutant of Escherichia coli with altered ribosomal protein component

Erythromycin combines with 50S ribosomal subunit of an erythromycin-sensitive Escherichia coli (strain Q13), while ribosomes from an erythromycin-resistant mutant from this strain have little affinity for the antibiotic. A protein component of the 50S subunit of the mutant strain is distinct from that of the parent Q13 strain.     

RNA-protein interactions in 30S ribosomal subunits: folding and function of 16S rRNA

Chemical probing methods have been used to "footprint" 16S ribosomal RNA (rRNA) at each step during the in vitro assembly of twenty 30S subunit ribosomal proteins. These experiments yield information about the location of each protein relative to the structure of 16S rRNA and provide the basis for derivation of a detailed model for the three-dimensional folding of 16S rRNA. Several lines of evidence suggest that protein-dependent conformational changes in 16S rRNA play an important part in the cooperativity of ribosome assembly and in fine-tuning of the conformation and dynamics of 16S rRNA in the 30S subunit.     

Distribution of protein and RNA in the 30S ribosomal subunit

In Escherichia coli, the small ribosomal subunit has a sedimentation coefficient of 30S, and consists of a 16S RNA molecule of 1541 nucleotides complexed with 21 proteins. Over the last few years, a controversy has emerged regarding the spatial distribution of RNA and protein in the 30S subunit. Contrast variation with neutron scattering was used to suggest that the RNA was located in a central core of the subunit and the proteins mainly in the periphery, with virtually no separation between the centers of mass of protein and RNA. However, these findings are incompatible with the results of efforts to locate individual ribosomal proteins by immune electron microscopy and triangulation with interprotein distance measurements. The conflict between these two views is resolved in this report of small-angle neutron scattering measurements on 30S subunits with and without protein S1, and on subunits reconstituted from deuterated 16S RNA and unlabeled proteins. The results show that (i) the proteins and RNA are intermingled, with neither component dominating at the core or the periphery, and (ii) the spatial distribution of protein and RNA is asymmetrical, with a separation between their centers of mass of about 25 angstroms.     

Crystal structure of the ribosome at 5.5 A resolution

We describe the crystal structure of the complete Thermus thermophilus 70S ribosome containing bound messenger RNA and transfer RNAs (tRNAs) at 5.5 angstrom resolution. All of the 16S, 23S, and 5S ribosomal RNA (rRNA) chains, the A-, P-, and E-site tRNAs, and most of the ribosomal proteins can be fitted to the electron density map. The core of the interface between the 30S small subunit and the 50S large subunit, where the tRNA substrates are bound, is dominated by RNA, with proteins located mainly at the periphery, consistent with ribosomal function being based on rRNA. In each of the three tRNA binding sites, the ribosome contacts all of the major elements of tRNA, providing an explanation for the conservation of tRNA structure. The tRNAs are closely juxtaposed with the intersubunit bridges, in a way that suggests coupling of the 20 to 50 angstrom movements associated with tRNA translocation with intersubunit movement.     

Structural roles for human translation factor eIF3 in initiation of protein synthesis

Protein synthesis in mammalian cells requires initiation factor eIF3, a approximately 750-kilodalton complex that controls assembly of 40S ribosomal subunits on messenger RNAs (mRNAs) bearing either a 5'-cap or an internal ribosome entry site (IRES). Cryo-electron microscopy reconstructions show that eIF3, a five-lobed particle, interacts with the hepatitis C virus (HCV) IRES RNA and the 5'-cap binding complex eIF4F via the same domain. Detailed modeling of eIF3 and eIF4F onto the 40S ribosomal subunit reveals that eIF3 uses eIF4F or the HCV IRES in structurally similar ways to position the mRNA strand near the exit site of 40S, promoting initiation complex assembly.     

Crystal structure of an initiation factor bound to the 30S ribosomal subunit

Initiation of translation at the correct position on messenger RNA is essential for accurate protein synthesis. In prokaryotes, this process requires three initiation factors: IF1, IF2, and IF3. Here we report the crystal structure of a complex of IF1 and the 30S ribosomal subunit. Binding of IF1 occludes the ribosomal A site and flips out the functionally important bases A1492 and A1493 from helix 44 of 16S RNA, burying them in pockets in IF1. The binding of IF1 causes long-range changes in the conformation of H44 and leads to movement of the domains of 30S with respect to each other. The structure explains how localized changes at the ribosomal A site lead to global alterations in the conformation of the 30S subunit.     

Crystal structure of the eukaryotic ribosome

Crystal structures of prokaryotic ribosomes have described in detail the universally conserved core of the translation mechanism. However, many facets of the translation process in eukaryotes are not shared with prokaryotes. The crystal structure of the yeast 80S ribosome determined at 4.15 angstrom resolution reveals the higher complexity of eukaryotic ribosomes, which are 40% larger than their bacterial counterparts. Our model shows how eukaryote-specific elements considerably expand the network of interactions within the ribosome and provides insights into eukaryote-specific features of protein synthesis. Our crystals capture the ribosome in the ratcheted state, which is essential for translocation of mRNA and transfer RNA (tRNA), and in which the small ribosomal subunit has rotated with respect to the large subunit. We describe the conformational changes in both ribosomal subunits that are involved in ratcheting and their implications in coordination between the two associated subunits and in mRNA and tRNA translocation.     

人核糖体40S亚基RPS11蛋白的原核表达和纯化

RPS11是核糖体小亚基40S的组成部分,属于核糖体蛋白S17p家族,由RPS11基因所编码,主要存在于真核生物中。本研究通过PCR扩增RPS11基因,构建pET43a-RPS11和pGEX-4T-1-RPS11原核表达载体。将重组质粒转入E.coli DH5α,序列测定正确后,将其转入E.coli BL21(DE3),加入IPTG诱导表达。表达蛋白经SDS-PAGE分析后,利用亲和层析法纯化蛋白。结果成功克隆RPS11基因,构建了原核表达载体pET43a-RPS11和pGEX-4T-1-RPS11,转化宿主菌E.coli BL21(DE3)中进行了表达。SDS-PAGE分析证实表达目的蛋白正确。通过Ni-TNA和GSH-Sepharose层析柱获得纯化蛋白,为进一步研究该蛋白的生物学功能奠定了基础。     

柑橘黄龙病菌 RAA-LDF 方法的建立

本研究基于柑橘黄龙病菌50S核糖体亚基基因的保守片段设计并合成引物和探针,通过对反应条件的优化建立了柑橘黄龙病菌重组酶聚合酶-侧流层析试纸条RAA-LDF检测方法,该方法可用于快速高效完成柑橘黄龙病菌检测,试验结果表明该方法灵敏度可达到100copies/uL,特异性试验结果显示除柑橘黄龙病菌基因组呈阴性外, 大肠杆菌、 金黄色葡萄球菌、胸膜肺炎放线杆菌、单核细胞增生李斯特菌、 支气管败血波氏杆菌、沙门氏菌均为阴性,特异性良好。利用该方法检测102 份柑橘叶样本,提取核酸后经过 RAA-LDF 检测法,结果显示 53 份样本核酸为阳性,49 份样本核酸为阴性,与PCR,RAA方法比较,弱阳的检出率偏低,但是 RAA-LDF 检测法摆脱仪器依赖,操作更简便快速,无需电泳检测,避免核酸扩增产物开盖污染的风险,适宜于柑橘黄龙病菌的快速检测,适合在基层使用。     

Structural biology. The ribosome is a ribozyme

Ribosomes, the cellular factories that manufacture proteins, contain both RNA and protein, but exactly how all of the different ribosomal components contribute to protein synthesis is still not clear. Now, as Thomas Cech explains in his Perspective, atomic resolution of the structure of the large ribosomal subunit reveals that, as predicted by those convinced of a prebiotic RNA world, RNA is the catalytic component with proteins being the structural units that support and stabilize it (Ban et al., Nissen et al., Muth et al.).     

Ribosome structure and function emergent

Although the corresponding data for 50S subunits are still being assembled, it is doubtful that these data will significantly alter the general features of ribosome structure that have emerged from analysis of the 30S subunits. One overwhelming characteristic of the ribosome is its apparent complexity, which is reflected both in the diversity of ribosomal components and in their dissymmetric arrangement. The absence of repeat-structures implies that the functions of the ribosome are dissymmetric; this should influence the choice of models for protein synthesis.     

低氧胁迫下斑马鱼鳃中核糖体蛋白基因家族的表达分析

为研究斑马鱼核糖体蛋白应对低氧胁迫的生物学功能，对低氧胁迫和常氧条件下斑马鱼（Danio rerio）鳃组织进行转录组分析，利用高通量测序检测了低氧胁迫与常氧条件下斑马鱼鳃转录组中核糖体蛋白家族基因的表达差异。结果表明：在两个不同浓度的低氧胁迫下，斑马鱼鳃组织中60个核糖体蛋白基因的表达量显著上调。其中大亚基核糖体蛋白基因35个，小亚基核糖体蛋白基因25个。在低氧胁迫下斑马鱼鳃中显著差异表达基因GO富集的前15条通路中，均包括核糖体蛋白基因，且其中的5条通路与核糖体蛋白组装合成相关。在富集到“translation”GO通路中，富集到44个核糖体蛋白基因。另外，利用前期筛选出的低氧条件下斑马鱼鳃中显著低表达的2个miRNAs，针对低氧下表达量显著上调的60个核糖体蛋白基因进行靶基因预测，结果表明：斑马鱼miR-455-3p可以同时靶向核糖体蛋白基因rpl13和rplp1来调控斑马鱼对低氧环境的适应。     

A complete mapping of the proteins in the small ribosomal subunit of Escherichia coli

The relative positions of the centers of mass of the 21 proteins of the 30S ribosomal subunit from Escherichia coli have been determined by triangulation using neutron scattering data. The resulting map of the quaternary structure of the small ribosomal subunit is presented, and comparisons are made with structural data from other sources.     

青海湖裸鲤核糖体蛋白S3a基因的克隆和表达特性研究

青海湖裸鲤是青海湖及其周边流域唯一的经济鱼类,在鱼-鸟-草地生态系统中处于核心地位。核糖体蛋白S3a（RPS3a）是真核细胞中核糖体40S小亚基的组成成分,为一种多功能性蛋白。开展青海湖裸鲤高盐适应机理的研究,有助于揭示青海湖裸鲤的基本生命活动规律,为该鱼种的资源保护和人工增殖放流提供理论依据。我们通过RT-PCR和RACE技术,得到了青海湖裸鲤RPS3a的完整编码序列［KC818610.1］。通过实时荧光定量检测胚胎发育不同阶段和不同盐度胁迫条件下RPS3a表达水平的变化,显示其在盐度胁迫条件下和胚胎发育过程中表达水平逐步上升,初步表明RPS3a对于青海湖裸鲤胚胎发育和盐度适应性生理机制的变化有着重要作用。     

The "spliceosome": yeast pre-messenger RNA associates with a 40S complex in a splicing-dependent reaction

The in vitro splicing reactions of pre-messenger RNA (pre-mRNA) in a yeast extract were analyzed by glycerol gradient centrifugation. Labeled pre-mRNA appears in a 40S peak only if the pre-mRNA undergoes the first of the two partial splicing reactions. RNA analysis after extraction of glycerol gradient fractions shows that lariat-form intermediates, molecules that occur only in mRNA splicing, are found almost exclusively in this 40S complex. Another reaction intermediate, cut 5' exon RNA, can also be found concentrated in this complex. The complex is stable even in 400 mM KCl, although at this salt concentration, it sediments at 35S and is clearly distinguishable from 40S ribosomal subunits. This complex, termed a "spliceosome," is thought to contain components necessary for mRNA splicing; its existence can explain how separated exons on pre-mRNA are brought into contact.