Crystalline transfer RNA: the three-dimensional Patterson function at 12-angstrom resolution

An orthorhombic form of crystalline formylmethionine transter RNA has been obtained which contains one molecule as the asymmetric unit of the unit cell. Three-dimensional x-ray diffraction data have been collected up to a resolution of 12 angstroms, and from this a Patterson function has been calculated. The function contains an elongated ridge of interatomic vectors parallel to the c-axis of the crystal. Analysis of the function suggests that the molecules are elogated and dimerized in an overlapping antiparrael fashion along the c-axis. The dimer has a length near 109 angstroms and a width of 35 angstroms in one direction. The individual molecular length is approximately 80 angstroms with an irregular cross section measuring 25 by 35 angstrms.     

Primary structure of the beta subunit of the DHP-sensitive calcium channel from skeletal muscle

Complementary DNAs for the beta subunit of the dihydropyridine-sensitive calcium channel of rabbit skeletal muscle were isolated on the basis of peptide sequences derived from the purified protein. The deduced primary structure is without homology to other known protein sequences and is consistent with the beta subunit being a peripheral membrane protein associated with the cytoplasmic aspect of the sarcolemma. The protein contains sites that might be expected to be preferentially phosphorylated by protein kinase C and guanosine 3',5'-monophosphate-dependent protein kinase. A messenger RNA for this protein appears to be expressed in brain.     

A single troponin T gene regulated by different programs in cardiac and skeletal muscle development

A cloned complementary DNA derived from a messenger RNA transiently present at low abundance levels in early chick embryonic skeletal muscle hybridizes to a messenger RNA present at high abundance levels in cardiac muscle. Genomic DNA hybridization and nucleotide sequence identity of complementary DNA's from both heart and skeletal muscle demonstrate that the messenger RNA's from both sources are encoded by the same gene. The encoded polypeptide is a troponin T sequence which is probably a cardiac isoform. This single copy troponin T isogene is governed by different regulatory programs in heart and skeletal muscle differentiation.     

Three-dimensional structure of poliovirus at 2.9 A resolution

The three-dimensional structure of poliovirus has been determined at 2.9 A resolution by x-ray crystallographic methods. Each of the three major capsid proteins (VP1, VP2, and VP3) contains a "core" consisting of an eight-stranded antiparallel beta barrel with two flanking helices. The arrangement of beta strands and helices is structurally similar and topologically identical to the folding pattern of the capsid proteins of several icosahedral plant viruses. In each of the major capsid proteins, the "connecting loops" and NH2- and COOH-terminal extensions are structurally dissimilar. The packing of the subunit "cores" to form the virion shell is reminiscent of the packing in the T = 3 plant viruses, but is significantly different in detail. Differences in the orientations of the subunits cause dissimilar contacts at protein-protein interfaces, and are also responsible for two major surface features of the poliovirion: prominent peaks at the fivefold and threefold axes of the particle. The positions and interactions of the NH2- and COOH-terminal strands of the capsid proteins have important implications for virion assembly. Several of the "connecting loops" and COOH-terminal strands form prominent radial projections which are the antigenic sites of the virion.     

糖皮质激素对肉鸡骨骼肌糖摄取能力的影响及机制探讨

利用同位素双标法,测定在NO供体硝普钠（SNP）、NO合酶（NOS）抑制剂N^G-硝基、L-精氨酸甲酯（L-NAME）和糖皮质激素皮质酮（corticosterone）存在条件下,基础状态或胰岛素诱导的肉鸡离体腓骨长肌的2-脱氧葡萄糖（2-DG）转运速率。结果表明：①SNP引起肌肉基础状态和胰岛素诱导的2-DG转运速率增加,表明NO是调节骨骼肌糖代谢的一个重要细胞因子。②皮质酮引起静态肌肉2-DG转运速率增加,可能与其破坏肌纤维膜的完整性有关。③皮质酮引起肌肉胰岛素诱导的2-DG转运速率下降,加入SNP后,胰岛素机能明显改善,表明应激早期,机体NO浓度的下降,可能与糖皮质激素诱发的胰岛素抵抗有一定关系。④与体内研究不同的是,没有观察到L-NAME对离体骨骼肌2-DG转运速率的影响,表明血液动力学因素在骨骼肌糖摄取机制中同样起着非常关键的作用。     

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.     

Three-dimensional structure of an antigen-antibody complex at 2.8 A resolution

The 2.8 A resolution three-dimensional structure of a complex between an antigen (lysozyme) and the Fab fragment from a monoclonal antibody against lysozyme has been determined and refined by x-ray crystallographic techniques. No conformational changes can be observed in the tertiary structure of lysozyme compared with that determined in native crystalline forms. The quaternary structure of Fab is that of an extended conformation. The antibody combining site is a rather flat surface with protuberances and depressions formed by its amino acid side chains. The antigen-antibody interface is tightly packed, with 16 lysozyme and 17 antibody residues making close contacts. The antigen contacting residues belong to two stretches of the lysozyme polypeptide chain: residues 18 to 27 and 116 to 129. All the complementarity-determining regions and two residues outside hypervariable positions of the antibody make contact with the antigen. Most of these contacts (10 residues out of 17) are made by the heavy chain, and in particular by its third complementarity-determining region. Antigen variability and antibody specificity and affinity are discussed on the basis of the determined structure.     

The atomic structure of Mengo virus at 3.0 A resolution

The structure of Mengo virus, a representative member of the cardio picornaviruses, is substantially different from the structures of rhino- and polioviruses. The structure of Mengo virus was solved with the use of human rhinovirus 14 as an 8 A resolution structural approximation. Phase information was then extended to 3 A resolution by use of the icosahedral symmetry. This procedure gives promise that many other virus structures also can be determined without the use of the isomorphous replacement technique. Although the organization of the major capsid proteins VP1, VP2, and VP3 of Mengo virus is essentially the same as in rhino- and polioviruses, large insertions and deletions, mostly in VP1, radically alter the surface features. In particular, the putative receptor binding "canyon" of human rhinovirus 14 becomes a deep "pit" in Mengo virus because of polypeptide insertions in VP1 that fill part of the canyon. The minor capsid peptide, VP4, is completely internal in Mengo virus, but its association with the other capsid proteins is substantially different from that in rhino- or poliovirus. However, its carboxyl terminus is located at a position similar to that in human rhinovirus 14 and poliovirus, suggesting the same autocatalytic cleavage of VP0 to VP4 and VP2 takes place during assembly in all these picornaviruses.     

德国美利奴羊胎儿期骨骼肌组织学结构发育特征研究

【目的】探究胎儿期绵羊肌纤维的形成与发育规律,揭示德国美利奴羊胎儿期骨骼肌的组织学生长发育特征。【方法】选择妊娠期第75天(D75)、第105天(D105)和第135天(D135)的胎羊,测定其体长、体高和体质量;采集背最长肌,进行组织切片和HE染色,统计不同发育阶段胎儿单位肌纤维数量、直径和密度;应用免疫组化方法研究不同发育阶段背最长肌中快/慢肌纤维的类型和密度。【结果】随着怀孕母羊妊娠时间的增加,从75~135d胎儿体质量增长近17倍,体长、体高增加近1.5倍;单位肌纤维数量总体呈先增加后减少的变化趋势,在105d时单位面积肌纤维数量最高;肌纤维直径于妊娠75~105d增长幅度较为平缓,105~135d增长速率明显变大;早中期发育主要以慢肌(Ⅰ型肌纤维)为主,后期发育主要以快肌(Ⅱ型肌纤维)为主。【结论】德国美利奴羊胎儿肌纤维数量在妊娠105d时达到峰值,且此时肌纤维数量基本恒定,是肌纤维从肌增生转为肌肥大发育的关键时期,早中期发育主要以慢肌(Ⅰ型肌纤维)为主,后期发育主要以快肌(Ⅱ型肌纤维)为主。     

清远麻鸡宰后肉质酸化现象的研究

为了探讨鸡宰后肌肉的酸化规律,选择了168日龄清远麻鸡的腿肌和胸肌为材料,分别检测了宰后不同时间点(45min、6h、12 h、18 h、24 h)肌肉的pH值,乳酸含量,己糖激酶、丙酮酸激酶和乳酸脱氢酶活性的变化.结果显示,己糖激酶和乳酸脱氢酶的活性变化与乳酸含量的变化相关,而丙酮酸激酶活性基本不变.乳酸含量6h后开始升高,12h后达到最大值,而pH值在屠宰后6h降到最低值,此后基本不变,表明肌肉中pH值的下降主要由乳酸含量的上升引起.     

不同来源SPF鸡群遗传纯度的分子检测

采用随机扩增多态性DNA(RAPD)技术从分子结构上研究了不同来源SPF鸡群的遗传纯度。结果表明 :不同来源SPF鸡群平均条带相似系数差异显著 ,反映了这些不同来源SPF鸡群间的遗传纯度有明显不同。     

珍禽贵妃鸡与三黄鸡肌肉品质比较研究

采集相同条件下饲养的贵妃鸡、三黄鸡的同侧胸肌、腿肌,分别测定并比较其肉质感官品质、常规化学组分和肌肉组织学指标,为贵妃鸡肉品质评价、育种及品种推广工作提供参考.结果显示,贵妃鸡的肌肉贮存损失、胸肌剪切力和肉色显著低于三黄鸡;贵妃鸡肌肉熟肉率、pH值、肌纤维密度、粗蛋白、粗脂肪和粗灰分含量均高于三黄鸡,而腿肌和胸肌的肌纤维直径、水分含量、腹脂率和皮下脂厚均低于三黄鸡,但差异不显著.总体上比较,贵妃鸡的肉品质优于三黄鸡,但肉色在今后的改良中应该重点突破.     

免疫亲和层析法分离鸡补体C3d蛋白研究

利用抗鸡C3 21肽抗体制备免疫亲和层析柱,对鸡补体C3d进行了分离,并采用间接酶联免疫吸附实验(间接ELISA),对洗脱液中的C3d组分进行了检测,以SDS-PAGE电泳方法对分离到的C3d进行了检测。结果表明,利用亲和柱层析能够分离得到纯度较高的C3d蛋白,为鸡血清中C3d的提取纯化提供了较为简便的方法。     

Molecular cloning of the chicken progesterone receptor

To define the functional domains of the progesterone receptor required for gene regulation, complementary DNA (cDNA) clones encoding the chicken progesterone receptor have been isolated from a chicken oviduct lambda gt11 cDNA expression library. Positive clones expressed antigenic determinants that cross-reacted with six monospecific antibodies derived from two independent sources. A 36-amino acid peptide sequence obtained by microsequencing of purified progesterone receptor was encoded by nucleotide sequences in the longest cDNA clone. Analysis of the amino acid sequence of the progesterone receptor deduced from the cDNA clones revealed a cysteine-rich region that was homologous to a region found in the estrogen and glucocorticoid receptors and to the avian erythroblastosis virus gag-erb-A fusion protein. Northern blot analysis with chicken progesterone receptor cDNA's indicated the existence of at least three messenger RNA species. These messages were found only in oviduct and could be induced by estrogens.     

秦川牛胎儿骨骼肌卫星细胞的分离培养

【目的】探索胎牛骨骼肌卫星细胞分离、培养、鉴定及基因转染的方法。【方法】分别采用Ⅰ型胶原酶消化、Ⅰ型胶原酶与胰蛋白酶二步消化及链霉蛋白酶消化法对胎牛骨骼肌卫星细胞进行培养,比较了3种不同分离方法所得细胞数及其存活率的差异;利用差速贴壁法和Percoll密度梯度离心相结合的方法纯化骨骼肌卫星细胞,对纯化后的细胞进行myostatin基因RT-PCR以及结蛋白(Desmin)免疫细胞化学染色鉴定,最后通过电转染法对纯化的骨骼肌卫星细胞进行EGFP基因转染研究。【结果】3种消化培养方法中,以链霉蛋白酶消化法分离得到的胎牛骨骼肌卫星细胞数显著高于其它2种方法(P0.05),但细胞存活率较低(P0.05);而采用Ⅰ型胶原酶与胰蛋白酶二步消化法可以得到相对较高的细胞数及存活率。利用差速贴壁和Percoll密度梯度离心相结合的方法可以得到纯化的骨骼肌卫星细胞;电转染法适用于骨骼肌卫星细胞的基因转染。【结论】建立了胎牛骨骼肌卫星细胞分离、培养、纯化、鉴定及基因转染的方法,为通过转基因方法改良秦川牛产肉性能研究奠定了基础。     

Crystal structure of a divalent metal ion transporter CorA at 2.9 angstrom resolution

CorA family members are ubiquitously distributed transporters of divalent metal cations and are considered to be the primary Mg2+ transporter of Bacteria and Archaea. We have determined a 2.9 angstrom resolution structure of CorA from Thermotoga maritima that reveals a pentameric cone-shaped protein. Two potential regulatory metal binding sites are found in the N-terminal domain that bind both Mg2+ and Co2+. The structure of CorA supports an efflux system involving dehydration and rehydration of divalent metal ions potentially mediated by a ring of conserved aspartate residues at the cytoplasmic entrance and a carbonyl funnel at the periplasmic side of the pore.     

The complete atomic structure of the large ribosomal subunit at 2.4 A resolution

The large ribosomal subunit catalyzes peptide bond formation and binds initiation, termination, and elongation factors. We have determined the crystal structure of the large ribosomal subunit from Haloarcula marismortui at 2.4 angstrom resolution, and it includes 2833 of the subunit's 3045 nucleotides and 27 of its 31 proteins. The domains of its RNAs all have irregular shapes and fit together in the ribosome like the pieces of a three-dimensional jigsaw puzzle to form a large, monolithic structure. Proteins are abundant everywhere on its surface except in the active site where peptide bond formation occurs and where it contacts the small subunit. Most of the proteins stabilize the structure by interacting with several RNA domains, often using idiosyncratically folded extensions that reach into the subunit's interior.     

Bacterial resistance to beta-lactam antibiotics: crystal structure of beta-lactamase from Staphylococcus aureus PC1 at 2.5 A resolution

beta-lactamases are enzymes that protect bacteria from the lethal effects of beta-lactam antibiotics, and are therefore of considerable clinical importance. The crystal structure of beta-lactamase from the Gram-positive bacterium Staphylococcus aureus PC1 has been determined at 2.5 angstrom resolution. It reveals a molecule of novel topology, made up of two closely associated domains. The active site is located at the interface between the domains, with the key catalytic residue Ser70 at the amino terminus of a buried helix. Examination of the disposition of the functionally important residues within the active site depression leads to a model for the binding of a substrate and a functional analogy to the serine proteases. The unusual topology of the secondary structure units is relevant to questions concerning the evolutionary relation to the beta-lactam target enzymes of the bacterial cell wall.