Dioxygen binds end-on to mononuclear copper in a precatalytic enzyme complex

Copper active sites play a major role in enzymatic activation of dioxygen. We trapped the copper-dioxygen complex in the enzyme peptidylglycine-alphahydroxylating monooxygenase (PHM) by freezing protein crystals that had been soaked with a slow substrate and ascorbate in the presence of oxygen. The x-ray crystal structure of this precatalytic complex, determined to 1.85-angstrom resolution, shows that oxygen binds to one of the coppers in the enzyme with an end-on geometry. Given this structure, it is likely that dioxygen is directly involved in the electron transfer and hydrogen abstraction steps of the PHM reaction. These insights may apply to other copper oxygen-activating enzymes, such as dopamine beta-monooxygenase, and to the design of biomimetic complexes.     

RNAi技术概述

RNAi(RNA interference)是指外源性双链RNA(dsRNA)能抑制细胞内与其序列同源的基因的表达。在进化上,这可能是生物调控基因表达及抵御病毒侵染或转座子诱导DNA突变的一种共有的生理机制。本文对RNAi技术进行介绍。     

A microRNA as a translational repressor of APETALA2 in Arabidopsis flower development

Plant microRNAs (miRNAs) show a high degree of sequence complementarity to, and are believed to guide the cleavage of, their target messenger RNAs. Here, I show that miRNA172, which can base-pair with the messenger RNA of a floral homeotic gene, APETALA2, regulates APETALA2 expression primarily through translational inhibition. Elevated miRNA172 accumulation results in floral organ identity defects similar to those in loss-of-function apetala2 mutants. Elevated levels of mutant APETALA2 RNA with disrupted miRNA172 base pairing, but not wild-type APETALA2 RNA, result in elevated levels of APETALA2 protein and severe floral patterning defects. Therefore, miRNA172 likely acts in cell-fate specification as a translational repressor of APETALA2 in Arabidopsis flower development.     

A cellular microRNA mediates antiviral defense in human cells

In eukaryotes, 21- to 24-nucleotide-long RNAs engage in sequence-specific interactions that inhibit gene expression by RNA silencing. This process has regulatory roles involving microRNAs and, in plants and insects, it also forms the basis of a defense mechanism directed by small interfering RNAs that derive from replicative or integrated viral genomes. We show that a cellular microRNA effectively restricts the accumulation of the retrovirus primate foamy virus type 1 (PFV-1) in human cells. PFV-1 also encodes a protein, Tas, that suppresses microRNA-directed functions in mammalian cells and displays cross-kingdom antisilencing activities. Therefore, through fortuitous recognition of foreign nucleic acids, cellular microRNAs have direct antiviral effects in addition to their regulatory functions.     

离体法在饲料复合酶配方筛选中的应用

通过模拟动物消化生理规律,采用胃蛋白酶盐酸溶液（ＰＰＳ）和猪小肠液（ＰＩＦ）两步处理为特点的离体法分别测定９种鸡复合酶饲料和９种猪复合酶饲料的能量消化率,从而筛选出最佳复合酶组织。结果表明,最佳鸡伺料复合酶组合为纤维素酶１号＋植酸酶２号＋蛋白酶３号＋淀粉酶２号,最佳猪伺料复合酶组合为纤维素酶３号＋植酸酶３＋蛋白酶３号。肉鸡伺养试验结果表明,最佳复合酶试验组较对照组平均日增重提高９．６０％,料肉比降低２６．１０％;仔猪伺养试验结果表明,最佳复合酶试验组较对照组平均日增重提高９．６０％,料肉比降低２６．１％;仔猪伺养试验结果表明,最佳复合酶试验组较对照组平均日增重增高１２．４７％,料肉比降低３．２１％。结果验证了离体法在筛选伺料复合酶组合中的可行性。     

Methylation as a crucial step in plant microRNA biogenesis

Methylation on the base or the ribose is prevalent in eukaryotic ribosomal RNAs (rRNAs) and is thought to be crucial for ribosome biogenesis and function. Artificially introduced 2'-O-methyl groups in small interfering RNAs (siRNAs) can stabilize siRNAs in serum without affecting their activities in RNA interference in mammalian cells. Here, we show that plant microRNAs (miRNAs) have a naturally occurring methyl group on the ribose of the last nucleotide. Whereas methylation of rRNAs depends on guide RNAs, the methyltransferase protein HEN1 is sufficient to methylate miRNA/miRNA* duplexes. Our studies uncover a new and crucial step in plant miRNA biogenesis and have profound implications in the function of miRNAs.     

RNAi技术及其应用

阐述了RNAi技术的研究历史、作用机制及其应用。     

一种植物RNAi双元载体的构建

[目的]为利用RNAi技术研究植物基因组功能奠定基础。[方法]通过PCR技术克隆一系列RNAi双元载体所需要的元件：绿色荧光蛋白基因（gfp）、花椰菜花叶病毒启动子（CamV35S）、氨基糖苷3＇-腺苷酰基转移酶基因（aada）、胭脂碱合成酶基因终止信号（nos）,并进行组装,在双元载体质粒pCAMBIAl301的基础上构建目的载体。[结果]通过7种中间载体的构建,最后成功得到双元载体质粒pHBMT14。[结论]该载体的成功构建为以后的植物基因组功能研究提供了技术平台。     

RNA干扰机制及其主要蛋白因子研究进展

RNA干扰(RNA interference, RNAi)是由双链RNA(double stranded RNA, dsRNA)分子介导的、在mRNA水平上关闭相应序列基因表达、使其沉默的过程。RNAi作为一种古老而保守的基因沉默机制,广泛存在于真核生物体内,在细胞的发育调控、抗病毒防御、修复遗传损伤、调节正常的基因等生命过程中起着重要的作用。RNAi机制可以分为3个阶段：启动阶段、效应阶段及扩增阶段。RNAi干扰相关的主要蛋白因子有Dicer酶、Argonaute(AGO) 蛋白家族和RNA依赖的RNA聚合酶(RNA\|dependent RNA polymerase, RdRP)。文章对RNAi机制及其相关主要蛋白因子进行简要综述。     

RNAi在现代医学研究中的应用

简述了RNAi的作用机制,围绕其在肿瘤治疗、病毒感染性疾病治疗方面的研究进展进行了探讨,并对该技术运用在现代医学研究的潜在问题及前景进行了简要阐述。     

植物microRNA研究进展

MicroRNAs(miRNAs)是一类内源非编码小RNA(sRNAs)。在植物中,由初级转录本(pri-miRNA)通过Dicer-like酶(DCL)加工,形成的长度约21~24ntRNAs。miRNA组装的沉默复合体(RISC),对互补mRNA(靶基因)可进行剪切、调控植物生长发育和胁迫应答等过程。文章对miRNAs的生物合成、鉴定和验证、作用机理和功能及在技术应用等方面进行综述。     

RNAi及其在害虫防治中的应用

RNA干扰(RNA interference,RNAi)是一种由非编码的小分子双链RNA引发的序列特异性转录后基因沉默现象,普遍存在于线虫、真菌、昆虫和动植物等多种生物中。近年来,RNAi技术在昆虫中的成功应用为一系列新颖的、环境友好的害虫防治策略提供了理论依据。文章综述了RNAi技术的作用机制、dsRNA吸收机制及在害虫防治等领域的研究成果,并展望了该技术的应用前景。     

RNAi的机制及其在研究中的应用

由RNA介导的干扰过程可抑制特异基因的表达。1998年华盛顿卡耐基研究院的Fire和马萨诸塞大学癌症中心的Mello首次将双链RNA（doublestrandedRNA,dsRNA）注入线虫,发现可诱导基因靶向专一性的基因表达沉默,且较单独注射正义链或反义链都要强10倍,同时这种现象也可在线虫中观察到,     

hpRNA的制备新方法及其在RNAi载体中的应用

[目的]验证制备新方法所获得的稳定hpRNA是否可用于RNAi载体的构建并达到基因表达干扰的效果。[方法]利用制备新方法(2μL DNA与8μL H_2O混匀,95℃5 min,37℃15 min)制备hpRNA,后采用REGS方法构建Zm MDAR RNAi载体,通过Grx1-ro GFP2和荧光实时定量PCR检测基因表达干扰的效果。[结果]利用制备新方法制备50 nt hpRNA。Zm MDAR基因的表达量变化和Grxl-ro GFP2探针的荧光比值变化表明hpRNA介导的干扰载体引起了原生质体氧化还原状态的变化。[结论]通过制备新方法所制备的hpRNA为RNAi载体所介导的干扰作用奠定基础。     

家兔中microRNA的研究进展

microRNA(miRNA)是一类内源性非编码单链RNA分子,通过与靶基因mRNA配对以指导其功能表达,在动物中扮演着重要的基因调节作用。研究表明,miRNA广泛参与调节动物的生长发育、生殖调控、新陈代谢和疾病发生等生命过程。本文综述了miRNA在家兔中的研究,例如促进肌肉细胞增殖分化、调节脂肪代谢和影响疾病发生等,探讨miRNA在家兔中的研究现状和发展方向,旨在为家兔遗传育种与繁殖提供理论依据。     

The molecular structure of a DNA-triostin A complex

The molecular structure of triostin A, a cyclic octadepsipeptide antibiotic, has been solved complexed to a DNA double helical fragment with the sequence CGTACG (C, cytosine; G, guanine; T, thymine; A, adenine). The two planar quinoxaline rings of triostin A bis intercalate on the minor groove of the DNA double helix surrounding the CG base pairs at either end. The alanine residues form hydrogen bonds to the guanines. Base stacking in the DNA is perturbed, and the major binding interaction involves a large number of van der Waals contacts between the peptides and the nucleic acid. The adenine residues in the center are in the syn conformation and are paired to thymine through Hoogsteen base pairing.     

A novel nucleoprotein complex at a replication origin

The viral protein p6, required for the protein-primed initiation of replication of Bacillus subtilis phage phi 29, forms a nucleoprotein complex at the viral replication origins that shows novel features. Deoxyribonuclease I and hydroxyl radical footprinting data, as well as the induction of positive supercoiling, support a model in which a DNA right-handed superhelix tightly wraps around a multimeric p6 core. The interaction occurs through the DNA minor groove. The activity of p6 not only requires the formation of the complex but also its correct positioning, indicating that the other proteins involved in the initiation of replication recognize, at a precise position, either the p6 core or the DNA conformational change induced by p6.