DNA polymerase required for rapid repair of x-ray--induced DNA strand breaks in vivo

A much higher yield of DNA single-strand breaks was obtained in the DNA polymerase-deficient mutant Escherichia coli K-12 pol A1 after a given dose of x-rays than had been found before in Escherichia coli. The increased yield of single-strand breaks was due to the absence of a rapid repair system, which had not been described in Escherichia coli K-12. This absence probably accounts for the x-ray sensitivity of the pol A1 mutant. The rapid repair system can be reversibly inhibited in pol+ cells.     

盐泽螺旋藻藻蓝蛋白裂合酶CpcS的分子克隆及功能研究

为研究盐泽螺旋藻（Spirulina subsalsa）藻蓝蛋白裂合酶SsCpcS的催化功能,首先通过PCR技术从S. subsalsa FACHB351基因组DNA中扩增藻蓝蛋白裂合酶的编码基因SscpcS,构建表达质粒pCDFDuet-SscpcS,然后再与脱辅基蛋白和色素合成酶表达质粒pETDuet-SscpcB-Ssho1::SspcyA共同转入大肠杆菌BL21（DE3）,并经IPTG（Isopropyl β-D-Thiogalactoside,异丙基硫代半乳糖苷）诱导重组合成藻蓝蛋白。PCR产物测序表明SscpcS扩增成功;双酶切检测和SDS-PAGE电泳分析表明质粒pCDFDuet-SscpcS构建成功,且能表达目的蛋白。重组藻蓝蛋白PCB-CpcB细胞产物为深蓝色;纯化后的色素蛋白展现620 nm的最大吸收峰和646 nm的最大荧光发射峰;色素蛋白通过锌离子染色,在紫外线照射下展现明显荧光。该研究成功克隆源自盐泽螺旋藻的藻蓝蛋白裂合酶SsCpcS的编码基因,其表达产物SsCpcS能有效催化藻蓝蛋白的生物合成。此研究为S. subsalsa藻蓝蛋白的重组合成及抗氧化试剂的研制奠定基础,也为探明盐泽螺旋藻中CpcS的催化机理提供科学依据。     

Structure of a NHEJ polymerase-mediated DNA synaptic complex

Nonhomologous end joining (NHEJ) is a critical DNA double-strand break (DSB) repair pathway required to maintain genome stability. Many prokaryotes possess a minimalist NHEJ apparatus required to repair DSBs during stationary phase, composed of two conserved core proteins, Ku and ligase D (LigD). The crystal structure of Mycobacterium tuberculosis polymerase domain of LigD mediating the synapsis of two noncomplementary DNA ends revealed a variety of interactions, including microhomology base pairing, mismatched and flipped-out bases, and 3' termini forming hairpin-like ends. Biochemical and biophysical studies confirmed that polymerase-induced end synapsis also occurs in solution. We propose that this DNA synaptic structure reflects an intermediate bridging stage of the NHEJ process, before end processing and ligation, with both the polymerase and the DNA sequence playing pivotal roles in determining the sequential order of synapsis and remodeling before end joining.     

Uracil DNA glycosylase activity is dispensable for immunoglobulin class switch

Activation-induced cytidine deaminase (AID) is required for the DNA cleavage step in immunoglobulin class switch recombination (CSR). AID is proposed to deaminate cytosine to generate uracil (U) in either mRNA or DNA. In the second instance, DNA cleavage depends on uracil DNA glycosylase (UNG) for removal of U. Using phosphorylated histone gamma-H2AX focus formation as a marker of DNA cleavage, we found that the UNG inhibitor Ugi did not inhibit DNA cleavage in immunoglobulin heavy chain (IgH) locus during CSR, even though Ugi blocked UNG binding to DNA and strongly inhibited CSR. Strikingly, UNG mutants that had lost the capability of removing U rescued CSR in UNG-/- B cells. These results indicate that UNG is involved in the repair step of CSR yet by an unknown mechanism. The dispensability of U removal in the DNA cleavage step of CSR requires a reconsideration of the model of DNA deamination by AID.     

大白菜RAPD反应条件的优化

RAPD是作物主要农艺性状分子标记及遗传多样性研究的一项重要技术。为了适应大白菜反应体系,本试验以大白菜品种413、96及其F1为试材,对影响RAPD扩增的模板DNA用量、Mg2+浓度、TaqDNA聚合酶浓度、dNTPs浓度、引物浓度等因素进行了优化,结果如下:20μl PCR反应体系,30 ng(1.5μl)DNA模板,3 mmol/L Mg2+,0.01 U/μl Taq DNA聚合酶,0.4 mmol/L dNTPs,0.8μmol/L引物为最佳反应浓度。     

吴茱萸ISSR-PCR反应体系优化

[目的]建立吴茱萸ISSR-PCR最佳反应体系。[方法]采用改良的CTAB法提取吴茱萸基因组DNA,研究模板DNA、dNTPs、Mg^2＋、引物（U834）、Taq DNA聚合酶的浓度对ISSR-PCR扩增结果的影响。[结果]20μl反应体系中含2μl 10×PCR buffer,0.15 mmol/LdNTPs,1.6 mmol/L Mg^2＋,0.4 mmol/L引物,20 ng模板DNA,1.2 U Taq DNA聚合酶。[结论]为研究吴茱萸种质资源遗传多样性和分子鉴定奠定了技术基础。     

丝瓜ISSR-PCR反应体系的建立

以丝瓜为试材,研究了ISSR-PCR反应体系的主要成分及退火温度、循环次数对丝瓜ISSR扩增结果的影响。结果表明:在20μl的反应体系中,Mg2+的用量为2 mmol/L,dNTPs浓度为0.2 mmol/L,引物的浓度为0.6μmol/L,TaqDNA聚合酶的用量为1 U,模板DNA的用量为30 ng,在适当的退火温度下,35个循环能得到清晰、多态性高的ISSR带谱。     

Deleted HTLV-I provirus in blood and cutaneous lesions of patients with mycosis fungoides.

Mycosis fungoides, a rare form of cutaneous T cell leukemia/lymphoma, is suspected of having a viral etiology on the basis of certain similarities to adult T cell leukemia, which is associated with human T cell leukemia/lymphoma virus type I (HTLV-I) infection. Cell lines were established from peripheral blood mononuclear cells (PBMC) of an HTLV-I-seronegative patient with mycosis fungoides. DNA hybridization analysis revealed the presence of HTLV-I-related sequences with unusual restriction endonuclease sites. Sequence analysis of subcloned fragments demonstrated the presence of a monoclonally integrated provirus with a 5.5-kilobase deletion involving large regions of gag and env and all of pol. Additional evidence for the presence of deleted proviruses was found by polymerase chain reaction (PCR) amplification of DNA from cutaneous lesions of five other HTLV-I-seronegative patients. The findings suggest that HTLV-I infection may be involved in the etiology of at least certain cases of mycosis fungoides.     

甘薯RAPD-PCR反应条件的优化

以徐薯22的基因组DNA作为PCR反应模板,以随机引物进行RAPD-PCR反应,通过设置ToqDNA聚合酶加量、MgCl2 浓度、dNTPs 浓度、模板DNA加量、引物加量的不同梯度,探索出一套适合甘薯RAPD-PCR的最优反应条件.试验结果表明,最优反应条件为反应体系25.0μL,2.5μL的PCR 10xBuffer、0.15U 的Taq DNA 聚合酶、3.0 nmol·μL-1的MgCl2、0.6 nmol·μL-1的dNTPs、40 ng的DNA模板、40 ng的RAPD引物.     

珍稀濒危竹种筇竹(Qiongzhuea tumidinoda)RAPD反应条件的优化

以宜宾筇竹为材料建立了筇竹RAPD反应优化体系,用于筇竹遗传多样性分析,以改进的CTAB法提取筇竹叶片总DNA,分别测试了镁离子浓度、dNTP浓度、引物浓度、模板DNA含量、DNA聚合酶量对反应结果的影响。通过对各因子的组合比较,建立了筇竹RAPD反应优化体系:20μL PCR反应体积,10×Taq酶配套缓冲液(2μL);1.25 U Taq酶;75 ng模板DNA;45 ng引物;1.88 mmol/L MgCl2;0.19 mmol/L dNTP。     

木质素合成酶COMT基因的PCR扩增条件优化

以2×CTAB法从欧美杨107号嫩叶提取的基因组DNA为试材,建立了木质素合成酶COMT基因的PCR扩增体系。通过对PCR反应的影响因子——模板DNA用量、dNTP浓度、DNA聚合酶量、引物浓度和退火温度进行优化,最终建立了扩增COMT的PCR优化体系为:在20μL的反应体系中,dNTP为2.5 pmol,引物各为5 pmol,模板为5 ng,Red TaqTMDNA聚合酶1.25 U,退火温度为51℃,可以扩增出清晰的扩增带。     

晒烟RAPD反应体系的优化

以晒烟苗期幼叶为试材,通过设置不同的模版DNA、引物、dNTP、Mg2+及Taq DNA聚合酶的浓度梯度,优化RAPD的反应条件,建立1个适合晒烟的比较稳定的RAPD反应体系。结果表明,适合晒烟RAPD的反应体系是在25μL反应体系中,含模板40ng;引物UBC-388 1.5μL;Mg2+1.6mM;dNTP 0.2mM;Taq酶1U。     

红景天种内遗传多样性分析AFLP方法建立

研究建立一种用于药用植物红景天种内遗传多样性分析的AFLP分子标记方法.以提取红景天(Rhodiola.rosea L)种基因组DNA为模板,25 μL酶切体系中采用两步双酶切(Mse I、EcoR I),在20 μL连接体系中采用T4连接酶,22℃连接过夜,50 μL体系预扩增,Taq Plus酶2.5 U,dNTP 160 μM,对应引物0.5 μM,10×PCR Buffer(含Mg2+) 4.5 μL,25 μL体系选择性扩增,Taq Plus酶1.5 U,dNTP 80 μM,对应引物 0.25 μM,10×PCR Buffer(含Mg2+) 2.5 μL.AFLP分子标记技术是一种快速、准确、稳定的药用植物红景天的种内遗传多样性分析手段.     

香蕉ISSR反应体系的建立

以35份香蕉品种为材料,采用正交设计L25(56)对PCR反应中的DNA质量浓度、TaqDNA聚合酶用量、Mg2+浓度、引物浓度、退火温度及甲酰胺浓度等6个因素在5个水平上进行了优化试验.建立了稳定的、可重复的香蕉ISSR最佳反应体系和PCR扩增参数.确定在25μL的反应体系中,DNA模板质量浓度为0.8 ng/μL,Mg2+浓度为1.5 mmol/L,dNTPs浓度为0.3 mmol/L,引物浓度为0.2μmol/L,Taq酶为1.25 U,退火温度为52℃.     

大花君子兰ISSR-PCR反应体系的建立与优化

以大花君子兰为材料研究了PCR反应体系的主要成分及退火温度对君子兰ISSR扩增结果的影响,并对影响PCR反应体系的主要成分及退火温度进行筛选和优化,确立了适合君子兰ISSR-PCR分析的最佳反应体系:在20μL的反应体系中,Mg2+为2.0 mmol/L,模板DNA用量为50 ng/μL,Taq酶0.4 U,dNTPs浓度为0.15 mmol/L,引物浓度为0.4 mmol/L。筛选出了13个适宜君子兰遗传分析的ISSR引物,确定最适宜退火温度为52~56℃。