Construction and characterization of the transformation-competent artificial chromosome (TAC) libraries of Leymus multicaulis

Transformation-competent artificial chromosome system is able to clone and transfer genes efficiently in plants.In order to clone genes highly tolerant to barley yellow dwarf virus(BYDV),Aphids,drought and salt from Leymus multicaulis,the two TAC genomic libraries I and II were constructed in vector pYLTAC17 and pYLTAC747H/sacB,which contain about 165000 and 236000 recombinant clones sepa-rately.The genome coverage of the two libraries was totally estimated to be about 3―5 haploid genome equivalents,as size selection of genomic DNA fragments was approximately from 9 to 300 kb.Clones of the genomic libraries were collected as bulked pools each containing 500 clones or so,stored in twelve 96-deep-well plates and then were gridding in triplicate onto a high-density colony hybridization filter with a 3×3 pattern using a GeneTAC?G3 arraying robot after being transferred manually into three 384-well plates.Meanwhile 2501 and 2890 clones of Library in pYLTAC17 and in pYLTAC747H/sacB were stored individually in fourteen 384-well plates and then were automatically gridding in duplicate onto a high-density colony hybridization filter with a 6×6 pattern after a replication of plates.Nineteen positive clones were detected by using the probe glutahione reductase gene of L.multicaulis.TAC libraries constructed here can be used to isolate genomic clones containing target genes,and to carry out genome walking for positional cloning.Once the target TAC clones were isolated,they could be immediately transferred into plant genomes with the Agrobacterium system.     

Isolation of recombinant field strains of Marek’s disease virus integrated with reticuloendotheliosis virus genome fragments

Two Marek's disease virus (MDV) field strains were isolated from chickens with tumors independently from Guangdong and Guangxi provinces, and it was confirmed that there were no co-infections with reticuloendotheliosis viruses (REV) in chicken embryo fibroblast cells (CEF) in indirect fluorescence antibody test (IFA) with REV-specific monoclonal antibodies. By dot blot hybridization and PCR of genomic DNA of MDV-infected CEF, it was indicated that LTR fragments of REV genome were integrated into genome of these two MDV field strains. To amplify and clone the integrated REV LTR with MDV sequence at the junction, 4 primers from REV LTR and 7 primers from MDV genome fragment with REV LTR insertion hot points were synthesized and 28 (4x7) pairs of primers (one from REV and another from MDV for each pair) were used in PCR while using the genomic DNA of both strains as the templates. The sequence data demonstrated that both recombinant field strains contained the same REV LTR inserted into MDV at the identical sites in US fragment of the genomes. From the above, it was speculated that both recombinant field MDVs were originated from a same recombinant virus and spread among chicken flocks in two provinces.     

Construction of a full bacterial artificial chromosome （BAC） library of Oryza sativa genome

We have constructed a full BAC library for the superior early indica variety of Oryza sativa,Guang Lu Ai 4.The MAX Efficiency DH10B with increased stability of inserts was used as BAC host cells.The potent pBelo BACII with double selection markers was used as cloning vector.The cloning efficiency we have reached was as high as 98%,and the transformation efficiency was raised up to 10^6 transformants/μg of large fragment DNA.The BAC recombinant transformants were picked at random and analyzed for the size of inserts,which turned out to be of 120 kb in length on average.We have obtained more than 20,000 such BAC clones.According to conventional probability equation,they covered the entire rice genome of 420,000 kb in length.The entire length of inserts of the library obtained has the 5-to 6-fold coverage of the genome.To our knowledge,this is the first reported full BAC library for a complex genome.     

Cloning and Sequence Analysis of Genome from the Inner Mongolia Strain of the Endogenous Betaretroviruses （enJSRV）

In order to amplify the complete genome of enJSRV from the strain of Inner Mongolia （enJSRV-NM）, we used enJSRV-specific and JSRV-specific DNA probes in dot blot hybridization. Seven pairs of primers were designed based on Genbank sequences. Seven fragments were obtained by PCR and were cloned into the PMD19-T vectors. The recombinant plasmids were sequenced and analyzed. The results showed that the genome was 7 942 bp in length and contained four overlapping open reading frames corresponding to the gag, pro, pol and env genes as well as an additional open reading frame （orf-x） that overlaps the 3＇ end of the pol gene. The nucleotide acid sequences of the enJSRV-NM loci were compared with the sequences of South Africa enJS56A1 strain （Accession No.AF153615） and USA JSRV21 strain （Accession No. AF105220）. The nucleotide acid identities were 99.2% and 92.3% respectively. Two zinc fingers were found in the NC region in the predicted amino acid sequence. However, the YXXM motif, which is a reliable molecular marker for the infectious exogenous virus, was not found in the TM region. It was found that the enJSRV-NM region was 90%-98% identical at the amino acid level to its exogenous infectious counterparts in most of the retroviral genome. This is the first nucleotide sequence of enJSRV reported in P.R China. The resource work has provided a wide range of information useful not only for expression genomics and annotation of genomic DNA sequence, but also for further research on the clinical diagnosis of OPA.     

中国首次分离的辛德毕斯病毒XJ-160病毒株感染性全基因组cDNA克隆的构建与分析

报告了中国首次分离的辛德毕斯病毒XJ-160株的感染性全基因组cDNA克隆的构建与鉴定。利用RT—PCR方法获得覆盖病毒全长基因组的cDNA片段,以低拷贝质粒pBR322作为骨架,将基因组cDNA置于SP6RNA聚合酶启动子之后,基因组3’末端带有35个连续的A,通过DNA重组技术组装成病毒基因组全长cDNA克隆。该克隆可在大肠杆菌DH5a中稳定扩增。经体外转录,RNA转录体转染BHK-21细胞,细胞发生病变,恢复病毒滴度达到10^7～10^8PFU／ml。全基因组cDNA克隆构建过程中引入的沉默突变(8453位核苷酸由C变为T)产生XbaⅠ酶切位点作为遗传标记,在子代恢复病毒的基因组中稳定存在。从细胞病变的特征、BHK-21细胞的空斑形态、病毒的抗原性、病毒在细胞中的生长动力学特征以及对乳鼠的致病性等方面比较,恢复病毒和亲本病毒XJ-160没有显著区别,提示获得了具有感染性的XJ-160病毒全长cDNA克隆。该病毒感染性全基因组cDNA克隆可以作为反向遗传学系统,为进一步研究病毒复制和致病机制,以及开发相应的载体表达系统提供分子生物学工具。     

犬瘟热病毒小熊猫株反向遗传系统的构建及其鉴定

以驯化致弱的犬瘟热病毒小熊猫株(Canine distemper virus,CDV)为模板,构建犬痘热病毒感染性cDNA克隆.对其全基因组序列测定后,用RT-PCR的方法获得组成全长基因的7个片段,通过酶切、拼接将7段CDVcDNA序列插入到真核表达载体pCI的MCS上,构建犬瘟热病毒小熊猫株的全长cDNA质粒(pCI-CDV-LP),同时分别克隆CDV小熊猫株N、P、L蛋白ORF构建三个辅助质粒.酶切鉴定和序列测定表明,pCI载体中插入的核酶及CDV cDNA序列正确无误,使用转染试剂Lipofectamine TM 2000将全长质粒和三个辅助质粒共转染中国仓鼠肾细胞(BSR),经RT-PCR、间接免疫荧光和病毒感染VERO-SLAM细胞试验鉴定,成功拯救出CDV小熊猫株,显示CDV小熊猫株反向遗传系统构建完成,为犬瘟热病毒致病机理及免疫研究奠定基础.     

1型鸭肝炎病毒CL株感染性分子克隆的构建

摘要：【目的】构建1型鸭肝炎病毒（DHV）的感染性克隆,用于研究其基因组的结构与功能。【方法】用RT-PCR方法扩增出覆盖整个1型鸭肝炎病毒CL株基因组3个忠实性片段,并按顺序组装进载体pBR322中,获得全长cDNA克隆（BR-CL）。将BR-CL在体外转录出的RNA转染鸭胚肾细胞,并传至第6代,利用RT-PCR方法和间接免疫荧光试验进行鉴定。将获得的子代病毒（CL-R）在SPF鸡胚上传代,观察鸡胚死亡及胚体病变情况。通过胶体金免疫电镜观察子代病毒粒子的形态。【结果】RT-PCR、间接免疫荧光和胶体金免     

茶尺蠖小RNA病毒全长cDNA克隆的构建

为了初步研究茶尺蠖小RNA病毒(Ectropis oblique picorna-like virus, EoPV)的复制机制,从被EoPV感染致死的茶尺蠖幼虫中分离并纯化病毒粒子,提取病毒RNA,根据已公布的EoPV核苷酸序列,利用基因组上单一的酶切位点,设计特异性引物,应用RT-PCR扩增出5个覆盖全长的片段。 随后采用融合PCR将5个片段拼接,最终将全长定向克隆到低拷贝质粒载体上,成功构建cDNA全长克隆p-EoPV。 双酶切及测序鉴定证明全长克隆构建成功。 与原序列比较发现,该克隆在氨基酸水平上有8个突变和1个缺失。 本研究为深入探讨EoPV病毒生物学特性、病毒复制机理等奠定了基础     

犬瘟热病毒CDV-3株感染性克隆的构建与鉴定

以国内商品化水貂犬瘟热病毒疫苗所用毒株CDV-3为模板,构建犬瘟热病毒感染性c DNA克隆,为犬瘟热病毒新型疫苗研制、致病机理研究提供理论基础。设计13对引物对其全基因组序列测定,分析单一酶切位点,将CDV-3的全长分5个片段进行RT-PCR扩增。经酶切拼接,将5个片段顺次插入到酶切位点改造后的真核载体pc DNA3.2的多克隆酶切位点处,同时在F1首端和F5末端分别加入锤头状核酶和丁型肝炎核酶序列,获得CDV-3株的全长c DNA质粒(pcDNA3.2-CDV-3)。构建表达CDV-3 N、P、L蛋白的3个辅助质粒。利用转染试剂Lipofectamine~(TM) 2000将全长质粒和3个辅助质粒共转染293T细胞,3 d后,将上清接种到Vero细胞。观察犬瘟热病毒典型合胞体病变,对重组病毒进行免疫荧光鉴定和标签鉴定。最后,比较wtCDV-3和rCDV-3的生长特性。全长质粒和辅助质粒的酶切鉴定和序列测序均正确。拯救的重组病毒能在Vero细胞上形成典型的合胞体病变,经RT-PCR、间接免疫荧光和电镜观察鉴定,证明成功拯救出重组病毒rCDV-3株。rCDV-3的病毒滴度最高达到10~(7.667) TCID_(50)/mL,比wtCDV-3的滴度10~(6.667) TCID_(50)/mL高出约10倍。rCDV-3感染Vero细胞后,迅速大量增殖,于感染后36 h达到最高病毒滴度。而wt CDV-3增殖平缓,感染后72 h时病毒含量达到最大。文中建立的高效CDV-3株反向遗传操作平台,为犬瘟热病毒新型疫苗研制和致病机理研究奠定基础。