Chemical synthesis of poliovirus cDNA: generation of infectious virus in the absence of natural template

Full-length poliovirus complementary DNA (cDNA) was synthesized by assembling oligonucleotides of plus and minus strand polarity. The synthetic poliovirus cDNA was transcribed by RNA polymerase into viral RNA, which translated and replicated in a cell-free extract, resulting in the de novo synthesis of infectious poliovirus. Experiments in tissue culture using neutralizing antibodies and CD155 receptor-specific antibodies and neurovirulence tests in CD155 transgenic mice confirmed that the synthetic virus had biochemical and pathogenic characteristics of poliovirus. Our results show that it is possible to synthesize an infectious agent by in vitro chemical-biochemical means solely by following instructions from a written sequence.     

Crystal structure of the rabies virus nucleoprotein-RNA complex

Negative-strand RNA viruses condense their genome into a helical nucleoprotein-RNA complex, the nucleocapsid, which is packed into virions and serves as a template for the RNA-dependent RNA polymerase complex. The crystal structure of a recombinant rabies virus nucleoprotein-RNA complex, organized in an undecameric ring, has been determined at 3.5 angstrom resolution. Polymerization of the nucleoprotein is achieved by domain exchange between protomers, with flexible hinges allowing nucleocapsid formation. The two core domains of the nucleoprotein clamp around the RNA at their interface and shield it from the environment. RNA sequestering by nucleoproteins is likely a common mechanism used by negative-strand RNA viruses to protect their genomes from the innate immune response directed against viral RNA in human host cells at certain stages of an infectious cycle.     

PB2蛋白E627V突变可增强H7N9病毒对小鼠的致病力

【背景】低致病性H7N9病毒自2013年在我国首次出现以来,研究发现其对家禽均呈现低致病力,对哺乳动物模型小鼠也不表现任何的致病力。但是,2015年在湖南分离的1株低致病性H7N9病毒(简称HuN/S40726),却对哺乳动物小鼠表现为高致病力。分析、推测导致该病毒对哺乳动物致病力改变的原因可能在于该病毒PB2蛋白E627V的改变。【目的】为了揭示该病毒致病力的变化原因以及对哺乳动物致病性增强的机制,提供人类H7N9病毒感染、危害增强风险预警,展开该研究。【方法】选取2013年低致病性H7N9病毒代表株(简称SH/S1053)和上述湖南HuN/S40726病毒,开展了哺乳动物致病力对比试验以及可能导致病毒发生致病力变化的相关基因位点对比分析。然后以HuN/S40726病毒为模式毒株,利用反向遗传学技术,成功建立了病毒的反向遗传操作系统;利用基因点突变技术定点突变了HuN/S40726病毒PB2蛋白的627位氨基酸,救获了重组病毒r HuN/S40726、r HuN/S40726-PB2/627E和r HuN/S40726-PB2/627K。通过小鼠感染模型评估了以上3株重组突变病毒对哺乳动物的致病力,分析了PB2蛋白627位氨基酸的突变对小鼠致病力的差异。然后通过构建HuN/S40726病毒及其突变病毒的聚合酶复合表达质粒系统,以SH/S1053病毒为背景毒株构建聚合酶复合表达质粒系统作为对照,使用双荧光素酶法检测了PB2蛋白627位氨基酸的不同突变体在293T细胞中的聚合酶活性,进一步分析PB2蛋白627位氨基酸影响病毒毒力的内在机制。【结果】通过哺乳动物致病力对比试验以及可能导致病毒发生致病力变化的相关基因位点对比分析,推测导致HuN/S40726病毒对哺乳动物致病力改变的原因可能在于该病毒PB2蛋白E627V的改变。重组救获病毒和突变株对小鼠致病性试验结果显示,PB2蛋白E627V的改变显著的增强了HuN/S40726病毒对小鼠的致病力,使得病毒MLD50由≥6.5 log10EID50变化为3.5 log10EID50,病毒毒力增强了至少1 000倍以上。聚合酶活性试验结果表明,无论是在33℃还是37℃下,PB2蛋白E627V的改变,显著提高了HuN/S40726病毒在哺乳动物细胞中的聚合酶活性,与病毒对小鼠的致病性增强呈正相关性。【结论】PB2蛋白627位氨基酸(V)决定了HuN/S40726病毒对小鼠的高致病力。PB2蛋白E627V的改变能够显著增强HuN/S40726病毒在哺乳动物细胞中的聚合酶活性,是引起HuN/S40726病毒对哺乳动物致病力的重要因素。     

海洋假交替单胞菌CI4菌株抗菌蛋白分离纯化的初步研究

将海洋假交替单胞菌Pseudoaltermonas sp.CI4菌株于VNSS液体培养基中培养,获得浓缩无细胞上清液,采用纸片扩散法检测其抗菌活性。结果表明,该菌株的胞外产物能够抑制从岩石表面分离的污损细菌S1菌株和其自身的生长。除去菌体培养液,用饱和度为70%的硫酸铵沉淀,所得的拮抗物粗提液对热部分敏感,对蛋白酶K和链霉蛋白酶敏感,其作用的活性pH稳定范围为5.0-9.0。粗提液经Sephadex G-200柱层析、DE-52纤维素离子交换柱层析,Microcon离心超滤管分级和聚丙烯酰胺凝胶电泳（SDS-PAGE）跟踪检测,得到电泳纯抗菌蛋白,其相对分子质量为37 200。     

Polyadenylic acid in Visna virus RNA

Visna virus 70S RNA contains long stretches of polyadenylic acid [poly(A)]. The homogeneity in length of poly(4) regions is observed in 70S RNA from visna virus and all RNA tumor viruses tested, and not with other types of RNA. By this criterion visna virus resembles RNA tumor viruses.     

RT-PCR和Digoxigenin标记的核酸探针检测鸡传染性支气管炎病毒试验研究

用２对已发表的引物和１对自行设计的引物对同一ＩＢＶＨ１２０株进行ＲＴ－ＰＣＲ，分别获得了Ｓ１基因上与引物设计相一致的１７２０ｂｐ，２２８ｂｐ，６０２ｂｐ，的扩增片段。用自行设计的引物对７个毒株（Ｈ１２０，Ｈ５２，Ｍ４１，Ｃｏｎｎ，Ｇｒａｙ，Ｔ，Ｈｏｌｔｅ）和５个分离株（宜毒，上毒，云毒，ＨＫ，１１８）的含毒尿囊液或纯化病毒进行ＲＴ－ＰＣＲ。结果除Ｈｏｌｔｅ株，２个分离株（宜毒，云毒）外，其余均被成功地扩增出６０２ｂｐ的片段。将ＩＢＶＨ１２０株０６ｋｂＰＣＲ产物用Ｄｉｇｏｘｉｇｅｎｉｎ标记为探针，分别与上述各ＩＢＶ毒株的核酸及其扩增产物进行核酸杂交，均呈现阳性反应，而该探针不与ＩＢＤＶ和ＮＤＶ的ＤＮＡ，ＥＤＳ－７６病毒的ＤＮＡ及正常鸡胚尿囊液抽提物反应。ＲＴ－ＰＣＲ和核酸杂交技术提供了直接从尿囊液中快速检测出病毒，作为诊断ＩＢＶ的新方法。     

Reversal of creatine kinase translational repression by 3' untranslated sequences

A subline of U937 cells (U937D) was obtained in which creatine kinase B (CK-B) messenger RNA was present and bound to ribosomes, but CK activity was undetectable. Transformation of U937D cells with retrovirus vectors that contain the 3' untranslated region (3' UTR) of CK-B messenger RNA exhibited CK activity with no change in abundance of CK-B mRNA. The 3' UTR formed a complex in vitro with a component of S100 extracts from wild-type cells. This binding activity was not detectable in S100 extracts from cells that expressed CK activity after transformation with the 3' UTR-containing vector. These results suggest that translation of CK-B is repressed by binding of a soluble factor or factors to the 3' UTR.     

Molecular cloning of complementary DNA encoding the avian receptor for vitamin D

Vitamin D3 receptors are intracellular proteins that mediate the nuclear action of the active metabolite 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]. Two receptor-specific monoclonal antibodies were used to recover the complementary DNA (cDNA) of this regulatory protein from a chicken intestinal lambda gt11 cDNA expression library. The amino acid sequences that were deduced from this cDNA revealed a highly conserved cysteine-rich region that displayed homology with a domain characteristic of other steroid receptors and with the gag-erbA oncogene product of avian erythroblastosis virus. RNA selected via hybridization with this DNA sequence directed the cell-free synthesis of immunoprecipitable vitamin D3 receptor. Northern blot analysis of polyadenylated RNA with these cDNA probes revealed two vitamin D receptor messenger RNAs (mRNAs) of 2.6 and 3.2 kilobases in receptor-containing chicken tissues and a major cross-hybridizing receptor mRNA species of 4.2 kilobases in mouse 3T6 fibroblasts. The 4.2-kilobase species was substantially increased by prior exposure of 3T6 cells to 1,25(OH)2D3. This cDNA represents perhaps the rarest mRNA cloned to date in eukaryotes, as well as the first receptor sequence described for an authentic vitamin.     

Homologous viral interference: induction by RNA from defective particles of vesicular stomatitis virus

The viral RNA isolated from the defective particles of vesicular stomatitis virus was capable of interfering with the replication of this virus in chick embryo cells. The data indicate that the interfering ability of the defective particles of this virus is due to their nucleic acid component.     

利用反向遗传操作技术拯救重组新城疫病毒

将新城疫病毒(Newcastle disease virus,NDV)Anhinga株的全长cDNA的克隆质粒以及L、P、NP的表达质粒共转染稳定表达T7 RNA聚合酶的BSRT7/5细胞,得到拯救病毒。通过RT-PCR扩增、酶切鉴定、测序验证拯救病毒中分子标签的存在,并通过血凝试验测定病毒的血凝效价、测定蚀斑形成单位确定病毒滴度,从而证明病毒拯救成功。新城疫病毒Anhinga株的拯救成功为该病毒进行结构基因研究和疫苗研制奠定了基础。     

马铃薯Y病毒的RT—PCR检测

通过两种方法提取了烟草病叶中PVY病毒的RNA,然后针对PVY~N的CP基因序列,设计合成了一对特异性引物,运用反转录PCR技术对提取的PVY－RNA进行了体外扩增,结果得到与预期大小相一致的780bp片段,而对照未得到任何产物,从而建立了运用RT－PCR手段检测植物中PVY的又一有效途径,并运用此方法对东北三省部分地区马铃薯种薯中PVY的带毒情况进行了检测。     

Activation of the DNA replication checkpoint through RNA synthesis by primase

When DNA replication is inhibited during the synthesis (S) phase of the cell cycle, a signaling pathway (checkpoint) is activated that serves to prevent mitosis from initiating before completion of replication. This replication checkpoint acts by down-regulating the activity of the mitotic inducer cdc2-cyclin B. Here, we report the relation between chromatin structure and induction of the replication checkpoint. Chromatin was competent to initiate a checkpoint response only after the DNA was unwound and DNA polymerase alpha had been loaded. Checkpoint induction did not require new DNA synthesis on the unwound template strand but did require RNA primer synthesis by primase. These findings identify the RNA portion of the primer as an important component of the signal that activates the replication checkpoint.