polypeptide是什么意思,polypeptide中文翻译,polypeptide发音、用法及例句

•polypeptide

polypeptide发音

[.pɔli'peptaid]

英：　　美：

polypeptide中文意思翻译

n.多肽, 缩多氨酸

polypeptide词形变化

异体字: polyparium |名词复数: polyparies |

polypeptide常见例句

1 、Triethanolamine polypeptide oleate is a surfactant that breaks up cerumen.───三乙醇胺油酸是一种多肽表面活性剂，打破了耳垢。

2 、Effects of "polypeptide 024" on Bel7402 cell line cell cycle were analyzed by FCM. infrastructure was determined by transmission electron micrograph.───应用人肝癌BEL-7402细胞株和其它人肿瘤细胞株及腹水型肝癌H_(22)荷瘤鼠观察小分子多肽024的抗肿瘤作用；

3 、Disintegrins are a kind of highly homologous polypeptide abstracted from snake venom, which contain an Arg-Gly-Asp (RGD) or Lys-Gly-Asp (KGD) sequence and plentiful cysteines, and the molecular weight is 5~9kD[1].───去整合素(disintegrins)是从蛇毒中提取的一类同源性很高的多肽,含有Arg-Gly-Asp(RGD)序列或Lys-Gly-Asp(KGD)序列,半胱氨酸含量丰富,分子量为5~9kD[1]。

4 、Gastrin releasing peptide ( GRP )-, somatostatin-, 5 -hydroxytryp-tamine ( 5 -HT ) -and avian pancreatic polypeptide ( APP ) -immunoreactive cells were observed in the proventriculus of Phalacrocorax carbo ( Linnaeus ) .───在鸬鹚(Phalacrocorax carbo Linnaeus)(俗称鱼膺)的前胃中发现了促胃泌素释放多肽(GRP)-、生长抑素(Somatostatin)-、5-羟色胺(5-HT)-和禽胰多肽(APP)-免疫反应细胞。

5 、The progress of the analysis of polypeptide drugs was reviewed, putting emphasis on bioactivity analysis, structure analysis and purity analysis.───介绍多肽药物的生物活性分析、结构分析、纯度分析的发展状况。

6 、I'm getting an anomalous molecular weight in the purified polypeptide chain.─── 我发现纯多肽链 的分子量有些异常

7 、What is the approximate molecular weight of a protein with 682 amino acid residues in a single polypeptide chain?───一含682个氨基酸残基的单个多肽链的大致分子量是多少?

8 、Four genesare orderly designated mai-MT, mai-KS1, mai-ACP, and mai-KS2.The length of mai-MT is 906 bp, encodes a putative polypeptide of 301 aminoacids.───Mai-MT基因长906 bp,编码301个氨基酸。

9 、Based on the findings, the technology for walnut polypeptide wine was probed.───在此基础上进行了核桃多肽酒工艺的研究。

10 、ACTH (adrenocorticotropic hormone)Polypeptide hormone made in the pituitary gland.───促肾上腺皮质激素:脑下垂体生成的调节肾上腺皮质活性的一种多胜激素。

11 、There are many kinds of amino acid, protein and polypeptide in the anticoagulating activity of Scorpion.───全蝎抗凝活性成分中含有多种氨基酸、蛋白质和多肽。

12 、The recent advances about the action of polypeptide growth factors on apoptosis and interstitial fibrosis in obstructive nephropathy are reviewed.───就近年来多肽生长因子在梗阻肾细胞凋亡、间质纤维化中起作用的研究进展作一综述.

13 、Gelatin is soluble polypeptide macromolecule in warm water,and has some kinds of necessary amino acids.───明胶是温水可溶的多肽高分子聚合物,含有人体所必需的多种氨基酸;

14 、To specify the genetic code for an amino acid or a polypeptide.───指定遗传密码确定氨基酸或多肽的遗传密码

15 、The invention relates to a nucleic acid controlling the expression of a useful polypeptide, particularly in the posterior silk glands of Bombyx mori .───本发明涉及指导目的蛋白质在家蚕后产丝腺细胞内特异表达的核酸。

16 、Methods The levels of Pituitary Ade nylate Cyclase Activiting Polypeptide (PACAP) in the plasma and Kidney organizes after brian trauma were determined by RIA.───方法提高建立大鼠脑损伤模型,用RIA方法测定血浆及肾组织匀浆中垂体腺苷酸环化酶激活肽含量。

17 、The viral capsid polypeptide of 34 nm virus particle of 22 000 dalton can be used as Lentinula edodes virus identification marker with SDS - polyacrylamide gel electrophoresis(SDS - PAGE) and silver staining.───应用十二烷基磺酸钠聚丙烯酰胺(SDS-PAGE)凝胶电泳分析香菇菌丝蛋白质,根据能否检出22 000道尔顿的34nm香菇病毒外壳蛋白带作为菌株是否带病毒的指标。

18 、Coconut, milk, honey, Soya bean oil, Rhizobium lotus, and plant energy polypeptide, etc.───椰子,牛奶,蜂蜜,大豆油，荷花根瘤菌,植物能量多肽。

19 、Human islet amyloid polypeptide，IAPP Elisa Kit...───人胰岛淀粉样多肽（IAPP）试剂盒；

20 、A 16-17kD bioactive polypeptide that had antibacterial against activities E. coli ML-35P and Pseudomonas aeruginosa ATCC65922 was purified from human LAK cells, which was named as HLP-**21. N-terminal sequence of HLP-**21 was PKRKAEGDAK.───从人LAK细胞酸溶性提取物中纯化出一多肽 ,Tricine SDS PAGE表观Mr 为 17× 10 3,命名为HLP **2 1(humanlymphocytepeptide) ,具有抗致病性大肠杆菌ML 35P及铜绿假单胞菌ATCC6 5 92 2的活性。

21 、Altogether, roughly 67% of HSA is helical, with a remainder in turns and extended polypeptide and a large number of disulphide bridges.───它总共约有67%的螺旋结构，还含有少量的转角结构和松散的多肽链。

22 、It contains Ginseng saponin, active polypeptide protein, moistening factor, plant tannins mask, cover the skin and give out nutrition and resistance to free-radical gradually.───含有人参皂苷、活性多肽蛋白、深层保湿因子、植物鞣质膜，覆盖肌肤表层，源源释放养分与抗自由基。

23 、Phage display random peptide library is a kind of polypeptide library developed by filamentous bacteriophages.───摘要噬菌体随机展示肽库是一类利用丝状噬菌体发展起来的多肽文库。

24 、Unique formula: Blood-cleaing Potent Reducer contains hirudin, an acid polypeptide which is effective in anti-coagulation and anti-thrombosis.───“血清王”的酸性多肽--水蛭素，具有抗凝、抗血栓等作用。

25 、HSP70 is known to assist the folding of nascent polypeptide chains, act as a molecular chaperone and mediate the repair and degradation of altered or denatured proteins.───HSP70作为分子伴侣在协助新生多肽链折叠,蛋白质复合体的装配,以及调节、修护和降解变性的蛋白质方面起着重要作用。

26 、The polypeptide compositions of thylakoid membrane were different not in some composition but in some content.───两优培九的类囊体膜并不是某些多肽组分存在差异，而是含量差异。

27 、Ru Zhen is comprised of bioactive protein and polypeptide which is extracted from colostrum.───乳珍是从母牛的初乳中提炼的生物活性蛋白及多肽。

28 、Sequence analysis of Gal-4 eDNA showed that the cDNA of Gal-4 gene con- sists of 321 bp,encoding Gal 4 polypeptide of 63 amino acids,which comprised of signal peptide with 20 amino acids at N'terminus,and mature peptide with 38 amino acids.───序列分析结果表明,获得的广西黄鸡Gal-4基因大小为321 bp,推导的Gal-4由63个氨基酸组成,其中N端20个氨基酸为信号肽,C端38个氨基酸组成Gal-4的成熟肽。

29 、The effects of the polypeptide growth factors on the function of the PDLC became a hot issue of the research on the regeneration of the periodontal tissues.───多肽生长因子对PDLC功能影响的研究成为牙周组织再生研究的热点之一。

30 、This course focuses on the mechanisms by which the amino acid sequence of polypeptide chains (proteins), determine their three-dimensional conformation.───本门课程着重在多肽（蛋白质）的氨基酸序列如何决定它的三维空间构型的机制。

31 、The peanut is one of the main economic crops and peanut polypeptide has vital physiological function.───摘要花生是我国主要的经济作物之一，花生多肽具有重要的生理功能。

32 、PolyPeptide Laboratories offers you a number of generic peptides, produced on an industrial scale under cGMP. Our generic peptides are being sold for the bulk market worldwide.───多肽实验室集团提供品种齐全的缩氨酸，可用于生物和药物研究。

33 、The anti-fatigue effect of low molecular weight level polypeptide of sea cucumber on mice was studied through different dose lavage.───摘要不同浓度的低分子量海参肽对小鼠灌胃，研究了海参肽对小鼠的抗疲劳作用。

34 、Tricine-SDS-PAGE showed that HPLC fraction 21 ( HLP-**21) that had potent antimicrobial activity was of a purified single polypeptide with a apparent molecular weight of 14 kDa.───将这三个组分用反向高效液相色谱技术进一步分离纯化，琼脂糖弥散法筛选纯化各组分的抗菌活性，较强抗菌活性的组分进行Tricine-SDS-PAGE电泳初步测定分子量及纯度。

35 、Glycoprotein is a kind of vital physicological active object, which is made from many covalent forms of polypeptide and oligosccharide.───摘要糖蛋白是由糖链与多肽链以多种形式共价修饰而形成的一类重要生理活性物质。

36 、Polypeptide A compound that contains many amino acids linked together by peptide bonds.───多肽：包含许多由肽键连接的氨基酸构成的化合物。

37 、A protein called a release factor binds directly to the stop codon, causing the addition of a water molecule instead of an amino acid to the polypeptide chain.───一种叫做释放因子的蛋白质直接结合在终止密码子上，导致一个水分子而不是氨基酸被加在肽链末端。

38 、The molecular component of a collagen fiber,consisting of three polypeptide chains coiled around each other.───原胶原(蛋白)胶原纤维之组成分子，由三条互相盘绕在一起的多肽链组成

39 、Any of various red, often toxic, polypeptide antibiotics obtained from soil bacteria.───放线菌素一种从土壤细菌中提取的红色的，通常是有毒的多肽抗生素

40 、Also, the modulation of polypeptide chain and solvent environment on secondary structure of peptide segment was discussed.───并讨论了蛋白质肽链和溶剂环境对肽段二级结构的调制作用。

41 、Active forms of Fuman EPF is mainly polypeptide of 21.2 KD and 26.3 KD.───早孕血清中EPF的活性形式主要为21.2KD、26.3KD的蛋白多肽;

42 、The foamy substances cover foam protein, polypeptide, isohumulone, melanoid, metal ions, amylase, alcohol and barm etc.───使啤酒形成泡沫的物质有泡沫蛋白和多肽、异葎草酮、类黑素、金属离子、多糖、酒精、二氧化碳及酵母等。

43 、A basic polypeptide antibiotic (trade name Viocin) administered intramuscularly (along with other drugs) in the treatment of tuberculosis.───一种多肽用来（和其他的药物一起）治疗肺结核疾病的多肽抗生素（商标是紫霉素）。

44 、The primary structure is concerned with the number and type of amino acids present and their sequence in the polypeptide chain.───初级结构与氨基酸数量和类型,以及它们在多肽链上的排列次序有关。

45 、The initiation codon represents the first amino acid, N-formyl methionine, at the N terminus of the polypeptide.───即编码多肽N-端第一个氨基酸即甲硫氨酸（N-甲酸化的）的密码子。

46 、Method The protein polypeptide was analysed in Gardenia jasminoides Ellis and Gardenia jasminoides Ellis var.grandiflora Nakai respectively by high-performance capillary electrophoresis(HPCE).───方法采用高效毛细管电泳法(HPCE)对栀子及其伪品水栀子蛋白多肽进行分析。

47 、Trefoil factor 1(TFF1), a member of the trefoil factor family, is a growth factor like small polypeptide.───三叶因子1(TFF1)属三叶因子家族,是近年来被人们注意到的具有胃肠道粘膜保护及修复作用的生长因子类小分子多肽物质。

48 、Basic single-chain polypeptide that inhibits numerous serine proteases by binding to the active site of the enzyme, form ing tight complexes.───基本的单链多肽，通过与酶的活性位点紧密结合形成复合物，抑制大多数的丝氨酸蛋白酶。

49 、It contains abundant dainty substances as nucleotide, guanylic acid, inosinic acid, polypeptide and amino acid, as well as plenty of vitamin B complex.───其核苷酸、鸟甘酸、肌苷酸及多肽和氨基酸等美味物质异常丰富，还含有大量的维生素B群。

50 、This product is made of the mixture of polynucieotide,aminoacid and polypeptide whose molecular weight is lower than 5000 Dalton.───本品系用健康猪脾或牛脾为原料，经细胞破碎超滤等工艺步骤提取的分子量小于5000道尔顿的多肽，氨基酸和多核苷酸的混合物。

51 、Given the occurrence of lit genes， it might be re-defined as the set of DNA sequences （exo ） that are required to produce a single polypeptide.───对分离的基因来说，它可被定义成一组需要用来产生蛋白质的脱氧核糖核酸序列，即外子。

52 、The oil system of its a gas for needing grasp system ratio contact quinonoid formula hermetic sealing wants to get the polypeptide in brief.───其所需的气体控制系统比接触式密封的油系统要简单得多。

53 、The ORF encoding p10 was 261 nucleotide long and encoding a putative 87 amino acid polypeptide of 9.3 kD.───P10基因编码区全长261bp，可编码分子量为9.3kD，由87个氨基酸残基组成的多肽。

54 、S1398 by orthogonal experimental design.The hydrolytic polypeptide was obtained.The debitter and destinking of the hydrolysis fluid and the precipitation were also studied.───S1398中性蛋白酶最佳水解工艺条件,并对制得的富含多肽的水解液的脱苦、脱腥及沉淀等问题进行了探讨。

55 、Endothelin is a kind of polypeptide generated by vascular endothelial cells and smooth muscle cells.───内皮素是一族由血管内皮细胞和平滑肌细胞产生的多肽。

56 、A polypeptide antibiotic obtained from a strain of a bacterium (Bacillus subtilis) and used as a topical ointment in the treatment of certain bacterial infections, especially those caused by cocci.───杆菌肽素：一种从菌系（模式种）中获得的多肽抗菌素，在对某种细菌传染病的治疗，尤指那些由球菌引起的传染病的治疗中用作局部软膏

57 、Ingredient: Collagen Protein, Ginkgo Extract, L-vitamin C, Biological Whitening Polypeptide, Lytic Keratinase, CY1100, Aquaxyl, Lactic Acid.───主要成份：胶原蛋白、银杏精华、左旋维生素C、生物美白多肽、溶角蛋白酶、CY1100、Aquaxyl、乳酸。

58 、Shenzhen, China. The company specializes in research, development and manufacture of polypeptide related products.───中国深圳专业从事多肽系列产品研究、开发和生产的高新技术企业。

59 、Lipase; enzyme immobilization; polypropylene microporous membrane;surface modification; glycopolymer; polypeptide; phospholipid analogous polymer;biphasic enzyme-membrane reactor.───01脂肪酶;酶固定化;聚丙烯微孔膜;表面改性;含糖聚合物;聚肽;类**脂聚合物;两相酶膜反应器

60 、A polypeptide antibiotic obtained from a strain of a bacterium(Bacillus subtilis) and used as a topical ointment in the treatment of certain bacterial infections, especially those caused by cocci.───枯草杆菌素一种从菌系（枯草芽孢杆菌属）中获得的多肽抗菌素，在对某种细菌传染病，尤指那些由球菌引起的传染病的治疗中用作局部软膏

61 、NCAM is a polypeptide first found in nerve tissue, which functions to involved in the signal transduction and loss of NCAM may cause high metastasis tendency of tumors cell.───NCAM 最初在神经组织中提取的多肽，它能起到传导信息，调控细胞生长的作用，它的丢失有可能使细胞的生长失控，与肿瘤**转移密切相关。

62 、It was observed that bovine pancreatic polypeptide (BPP) inhibited cysteamine-induced duodenal ulcers, and prevented cysteamine-induced SRIF depletion in duodenal mucosa in rats.───本工作发现,腹腔注射牛胰多肽可以减轻半胱胺引起的大鼠十二指肠溃疡,还可防止半胱胺引起的大鼠十二指肠粘膜生长抑素含量的下降。

63 、At the same time, the tolerant ecotype appeared, the heavy-metal-binding polypeptide produced, heavy metal compartmented and the free radical clear system activated.───植物的耐性机制表现在耐重金属生态型的产生、重金属结合多肽的形成、重金属离子的区域化以及活性氧自由基清除系统的活化.

64 、Nisin, an effective, harmless and natural bio-preservative, is a kind of polypeptide produced by Streptococcus lactisand can protect the food being spoiled by G+ bacteria.───乳链菌肽是某些乳链球菌产生的一种多肽物质,对引起食品腐败的大多数革兰氏**菌有很好的抑制作用,是一种高效、无毒副作用的天然生物防腐剂。

65 、The polypeptide chain forms a helix with 3.6 amino acid residues per turn and a pitch of 0.54nm.───多肽链上每转3.6个氨基酸残基形成一个螺旋,螺距为0.54nrn。

66 、Some proteins consist of more than one polypeptide chain, and the association of these subunits in the protein gives rise to the quaternary structure.───一些蛋白质不只是由一个多肽链组成的,并且这些蛋白质亚基的结构产生了四级结构的。

67 、FGFR3, a member of polypeptide growth factor family, is a tyrosine kinase receptor.───FGFR3是这一多肽类生长因子的家族成员之一，它是一种酪氨酸激酶受体。

68 、The anti-fatigue effects of sea encumber polypeptide on mice was studied at different dose.───摘要通过采用不同浓度的海参肽灌胃，研究海参肽对小鼠的抗疲劳作用。

69 、Liquor bitterness is induced mainly by fusel alcohols, aldehydes, phenolic compounds, sulphocompounds, alkaloid, polypeptide, amino acids, and inorganic salts.───摘要引起白酒苦味的主要物质为杂醇类、醛类、酚类化合物、含硫化合物、生物碱、多肽、氨基酸、无机盆。

70 、At the same time, mice in the peanut polypeptide treatment groups were orally given peanut polypeptide in the dosage of 400mg/kg bw and 800mg/kg bw, respectively.───多肽组分别用花生多肽水溶液灌胃(400、800mg/kgbw),实验周期32d。

71 、Gelatin is soluble polypeptide macromolecule in warm water, and has some kinds of necessary amino acids.───明胶是温水可溶的多肽高分子聚合物，含有人体所必需的多种氨基酸；

72 、The full length cDNA of ANGPTL4 consists of 1943 nucleotides in which there is a 1218 bp ORF encoding a 406-amino acid polypeptide (predicted molecular mass is 45.2 kDa).───并用RACE-PCR获得其全长。该基因cDNA全长为1943 bp，开放阅读框含1218 bp，编码406个氨基酸，预测分子量为45.2 kDa。

73 、A polypeptide antibiotic obtained from a strain of a bacterium(Bacillus subtilis) and used as a topical ointment in the treatment of certain bacterial infections,especially those caused by cocci.───枯草杆菌素，一种从菌系（枯草芽孢杆菌属）中获得的多肽抗菌素，在对某种细菌传染病，尤指那些由球菌引起的传染病的治疗中用作局部软膏。

74 、The candidate protein was identified as CTGF,a member of CCN polypeptide super-family.───所获取的候选蛋白为CTGF,是CCN多肽家族成员。

75 、The chemical constituents of grub ( Holotrichia diomphalia Bates. ) were systematically analyzed. The results showed that grab contained amino acids, polypeptide or protein, carbohydrate, alkaloid, organic acid, steroid et al.───对Holotrichia diomphalia Bates(蛴螬)的水浸液、乙醇提取液、石油醚提取液进行了成分分析,结果表明蛴螬中含有氨基酸、多肽或蛋白质、糖类、生物碱、有机酸盐、甾体化合物等成分。

76 、Levels of Pituitary Ade nylate Cyclase Activiting Polypeptide (PACAP) in the plasma of rat with brian trauma increased significantly,but in the Kidney organizes decreased markedly.───大鼠脑外伤组血浆垂体腺苷酸环化酶激活肽含量明显高于对照组,而肾组织匀浆中垂体腺苷酸环化酶激活肽含量明显低于对照组。

77 、The molecular component of a collagen fiber, consisting of three polypeptide chains coiled around each other.───原胶原（蛋白）胶原纤维之组成分子，由三条互相盘绕在一起的多肽链组成

78 、The s271 homolog isolated was a partial cDNA sequence and also encoded a polypeptide homologous to an Arabidopsis protein.───5271的同源序列的编码区不完整，所编码的多肤与拟南芥一个未知蛋白同源.

79 、Hydrolyzing deer placenta under this condition, hydrolyzation degree is 34.5%, getting rate of polypeptide is 81.56%.───在此条件下对鹿**进行水解，水解度达34.5%，多肽得率达81.56%。

80 、This paper reviews two basic types of epitope presentation and polypeptide expression systems, and discusses the development and application prospect of plant virus vector.───文章主要介绍了抗原展示系统和多肽表达系统，并分别列举一些植物病毒作为表达载体的研究进展情况以及应用前景。

81 、These results revealed that STFC was a polypeptide with M.W. of 12,870 dalton.───实验结果表明,TF_(HSV-1)特异成分是12,870 dalton的多肽。

trna如何决定其功能？

tRNA为Transfer_RNA的简称，又称转运RNA、转移RNA，是小RNA分子，能够在转译时，携带特定的氨基酸到正再加上氨基酸的多肽链(polypeptide chain)的ribosomal site上。 扩展资料

tRNA能认得特定的密码子，有个能使氨基酸接附在其上的位置。藉由反密码子使得每个tRNA能辨识的密码子均不同。（反密码子包含一段与mRNA上一段互补的序列）每个tRNA分子理论上只能与一种氨基酸接附，但是遗传密码有简并性（degenerate），使得有多于一个以上的tRNA可以跟一种氨基酸接附。 按照Francis Crick的假设，tRNA是一种“适配”分子，介导mRNA序列上密码子的'识别，并且翻译成相应的氨基酸。 类携带激活氨基酸，将它带到蛋白质合成部位并将氨基酸整合到生长着的肽链上的RNA。tRNA含有能识别模板mRNA上互补密码的反密码。

它既是运载活化型氨基酸（由胞液至核糖体上），又是识别mRNA分子中密码子的工具。一种氨基酸常可由数种特定的tRNA来运载，速度较快。tRNA这种功能是由于其特殊的结构所决定的。tRNA 3'端有一共同结构为—C—C—A。在A的第三碳原子上的OH基可与活性氨基酸结合。其另一端是反密码环，中间有三个相邻的核苷酸组成的反密码子，按碱基互补原则去辨认mRNA分子的密码子位置，从而保证了各种氨基酸准确无误的按顺序进入蛋白质肽链中去。

农杆菌的背景资料

Agrobacterium tumefaciens

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Agrobacterium tumefaciens

A. tumefaciens attaching itself to a carrot cell

Conservation status

Secure

Scientific classification

Kingdom: Bacteria

Phylum: Proteobacteria

Class: Alpha Proteobacteria

Order: Rhizobiales

Family: Rhizobiaceae

Genus: Agrobacterium

Species: A. tumefaciens

Binomial name

Agrobacterium tumefaciens

Smith & Townsend, 1907

Synonyms

Bacterium tumefaciens Smith and Townsend 1907

Pseudomonas tumefaciens (Smith and Townsend 1907) Duggar 1909

Phytomonas tumefaciens (Smith and Townsend 1907) Bergey et al. 1923

Polymonas tumefaciens (Smith and Townsend 1907) Lieske 1928

Agrobacterium tumefaciens is the causal agent of crown gall disease (the formation of tumours) in over 140 species of dicot. It is a rod shaped, Gram negative soil bacterium (Smith et al., 1907). Symptoms are caused by the insertion of a small segment of DNA (known as the T-DNA, for 'transfer DNA') into the plant cell,[1] which is incorporated at a semi-random location into the plant genome.

Agrobacterium tumefaciens (or A. tumefaciens) is an alphaproteobacterium of the family Rhizobiaceae, which includes the nitrogen fixing legume symbionts. Unlike the nitrogen fixing symbionts, tumor producing Agrobacterium are pathogenic and do not benefit the plant. The wide variety of plants affected by Agrobacterium makes it of great concern to the agriculture industry[2].

Economically, A. tumefaciens is a serious pathogen of walnuts, grape vines, stone fruits, nut trees, sugar beets, horse radish and rhubarb.

Contents [hide]

1 Conjugation

2 Method of infection

2.1 Formation of the T-pilus

2.2 Transfer of T-DNA into plant cell

3 Genes in the T-DNA

3.1 Hormones

3.2 Opines

4 Beneficial uses

5 References

6 External links

[edit] Conjugation

In order to be virulent, the bacterium must contain a tumour-inducing plasmid (Ti plasmid or pTi), of 180 kb, which contains the T-DNA and all the genes necessary to transfer it to the plant cell. Many strains of A. tumefaciens do not contain a pTi.

Since the Ti plasmid is essential to cause disease, pre-penetration events in the rhizosphere occur to promote bacterial conjugation - exchange of plasmids amongst bacteria. In the presence of opines, A. tumefaciens produces a diffusible conjugation signal called 30C8HSL or the Agrobacterium autoinducer. This activates the transcription factor TraR, positively regulating the transcription of genes required for conjugation.

[edit] Method of infection

The Agrobacterium tumefaciens infects the plant through its Ti plasmid. The Ti plasmid integrates a segment of its DNA, known as T-DNA, into the chromosomal DNA of its host plant cells.

A. tumefaciens have flagella that allow them to swim through the soil towards photoassimilates that accumulate in the rhizosphere around roots. Chemotaxis: reaction of orientation and locomotion to chemical attractants. Without chemotaxis there will be no cell-cell contact. Some strains may chemotactically move towards chemical exudates coming out from wounded plant such as acetosyringone and sugars. Acetosyringone is recognised by the VirA protein, a transmembrane protein encoded in the virA gene on the Ti plasmid. Sugars are recognised by the chvE protein, a chromosomal gene-encoded protein located in the periplasmic space.[3].

Induction of vir genes: At least 25 vir genes on Ti plasmid are necessary for tumor induction.In addition to their perception role, virA and chvE induce other vir genes. The VirA protein has a kinase activity, it phosphorylates it self on a histidine residu. Then the VirA protein phosphorylates the VirG protein on its aspartate residu.The VirG protein is a cytoplasmic protein traduced from the virG Ti plasmid gene, it's a transcription factor. It induces the transcription of the vir operons. ChvE protein regulates the second mecanism of vir genes activation. It increases VirA protein sensibility to phenolic compounds.[4]

Attachment is a two step process. Following an initial weak and reversible attachment, the bacteria synthesize cellulose fibrils that anchor them to the wounded plant cell. Four main genes are involved in this process: chvA, chvB, pscA and att. It appears that the products of the first three genes are involved in the actual synthesis of the cellulose fibrils. These fibrils also anchor the bacteria to each other, helping to form a microcolony.

After production of cellulose fibrils a Ca2+ dependent outer membrane protein called rhicadhesin is produced, which also aids in sticking the bacteria to the cell wall. Homologues of this protein can be found in other Rhizobia species.

Possible plant compounds, that initiate Agrobacterium to infect plant cells:[5]

Acetosyringone: Phenolic compound

alpha-Hydroxyacetosyringone

Catechol

Ferulic acid

Gallic acid

p-Hydroxybenzoic acid

Protocatechuic acid

Pyrogallic acid

Resorcylic acid

Sinapinic acid

Syringic acid

Vanillin

[edit] Formation of the T-pilus

In order to transfer the T-DNA into the plant cell A. tumefaciens uses a Type IV secretion mechanism, involving the production of a T-pilus.

The VirA/VirG two component sensor system is able to detect phenolic signals released by wounded plant cells, in particular acetosyringone. This leads to a signal transduction event activating the expression of 11 genes within the VirB operon which are responsible for the formation of the T-pilus.

First, the VirB" pro-pilin is formed. This is a polypeptide of 121 amino acids which requires processing by the removal of 47 residues to form a T-pilus subunit. The subunit is circularized by the formation of a peptide bond between the two ends of the polypeptide.

Products of the other VirB genes are used to transfer the subunits across the plasma membrane. Yeast two-hybrid studies provide evidence that VirB6, VirB7, VirB8, VirB9 and VirB10 may all encode components of the transporter. An ATPase for the active transport of the subunits would also be required.

[edit] Transfer of T-DNA into plant cell

A: Agrobacterium tumefaciens

B: Agrobacterium genome

C: Ti Plasmid : a: T-DNA , b: Vir genes , c: Replication origin , d: Opines catabolism genes

D: Plant cell

E: Mitochondria

F: Chloroplast

G: NucleusThe T-DNA must be cut out of the circular plasmid. A VirD1/D2 complex nicks the DNA at the left and right border sequences. The VirD2 protein is covalently attached to the 5' end. VirD2 contains a motif that leads to the nucleoprotein complex being targeted to the type IV secretion system (T4SS).

In the cytoplasm of the recipient cell, the T-DNA complex becomes coated with VirE2 proteins, which are exported through the T4SS independently from the T-DNA complex. Nuclear localization signals, or NLS, located on the VirE2 and VirD2 are recognised by the importin alpha protein, which then associates with importin beta and the nuclear pore complex to transfer the T-DNA into the nucleus. VIP1 also appears to be an important protein in the process, possibly acting as an adapter to bring the VirE2 to the importin. Once inside the nucleus, VIP2 may target the T-DNA to areas of chromatin that are being actively transcribed, so that the T-DNA can integrate into the host genome.

[edit] Genes in the T-DNA

[edit] Hormones

In order to cause gall formation, the T-DNA encodes genes for the production of auxin or indole-3-acetic acid via the IAM pathway. This biosynthetic pathway is not used in many plants for the production of auxin, so it means the plant has no molecular means of regulating it and auxin will be produced constitutively. Genes for the production of cytokinins are also expressed. This stimulates cell proliferation and gall formation.

[edit] Opines

The T-DNA contains genes for encoding enzymes that cause the plant to create specialized amino acids which the bacteria can metabolize, called opines.[6] Opines are a class of chemicals that serve as a source of nitrogen for A. tumefaciens, but not for most other organisms. The specific type of opine produced by A. tumefaciens C58 infected plants is nopaline (Escobar et al., 2003).

Two nopaline type Ti plasmids, pTi-SAKURA and pTiC58, were fully sequenced. A. tumefaciens C58, the first fully sequenced pathovar, was first isolated from a cherry tree crown gall. The genome was simultaneously sequenced by Goodner et al.[7] and Wood et al.[8] in 2001. The genome of A. tumefaciens C58 consists of a circular chromosome, two plasmids, and a linear chromosome. The presence of a covalently bonded circular chromosome is common to Bacteria, with few exceptions. However, the presence of both a single circular chromosome and single linear chromosome is unique to a group in this genus. The two plasmids are pTiC58, responsible for the processes involved in virulence, and pAtC58, coined the “cryptic” plasmid.[7][8]

The pAtC58 plasmid has been shown to be involved in the metabolism of opines and to conjugate with other bacteria in the absence of the pTiC58 plasmid.[9] If the pTi plasmid is removed, the tumor growth that is the means of classifying this species of bacteria does not occur.

[edit] Beneficial uses

Plants that have undergone transformation with Agrobacterium.The DNA transmission capabilities of Agrobacterium have been extensively exploited in biotechnology as a means of inserting foreign genes into plants. Marc Van Montagu and Jeff Schell, (University of Ghent and Plant Genetic Systems, Belgium) discovered the gene transfer mechanism between Agrobacterium and plants, which resulted in the development of methods to alter Agrobacterium into an efficient delivery system for genetic engineering in plants.[10] The plasmid T-DNA that is transferred to the plant is an ideal vehicle for genetic engineering.[11] This is done by cloning a desired gene sequence into the T-DNA that will be inserted into the host DNA. This process has been performed using firefly luciferase gene to produce glowing plants. This luminescence has been a useful device in the study of plant chloroplast function and as a reporter gene.[12] It is also possible to transform Arabidopsis by dipping their flowers into a broth of Agrobacterium, the seed produced will be transgenic. Under laboratory conditions the T-DNA has also been transferred to human cells, demonstrating the diversity of insertion application.[13]

The mechanism by which Agrobacterium inserts materials into the host cell by a type IV secretion system, is very similar to mechanisms used by pathogens to insert materials (usually proteins) into human cells by type III secretion. It also employs a type of signaling conserved in many Gram-negative bacteria called quorum sensing. This makes Agrobacterium an important topic of medical research as well.