?polypeptide

polypeptide發(fā)音

[.pɔli'peptaid]

英：　　美：

polypeptide中文意思翻譯

n.多肽, 縮多氨酸

polypeptide詞形變化

異體字: polyparium | 名詞復數: polyparies |

polypeptide常見(jiàn)例句

1 、Triethanolamine polypeptide oleate is a surfactant that breaks up cerumen.───三乙醇胺油酸是一種多肽表面活性劑，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.───應用人肝癌BEL-7402細胞株和其它人腫瘤細胞株及腹水型肝癌H_(22)荷瘤鼠觀(guān)察小分子多肽024的抗腫瘤作用；

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)是從蛇毒中提取的一類(lèi)同源性很高的多肽,含有Arg-Gly-Asp(RGD)序列或Lys-Gly-Asp(KGD)序列,半胱氨酸含量豐富,分子量為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 ) .───在鸕鶿(Phalacrocorax carbo Linnaeus)(俗稱(chēng)魚(yú)膺)的前胃中發(fā)現了促胃泌素釋放多肽(GRP)-、生長(cháng)抑素(Somatostatin)-、5-羥色胺(5-HT)-和禽胰多肽(APP)-免疫反應細胞。

5 、The progress of the analysis of polypeptide drugs was reviewed, putting emphasis on bioactivity analysis, structure analysis and purity analysis.───介紹多肽藥物的生物活性分析、結構分析、純度分析的發(fā)展狀況。

6 、I'm getting an anomalous molecular weight in the purified polypeptide chain.─── 我發(fā)現純多肽鏈 的分子量有些異常

7 、What is the approximate molecular weight of a protein with 682 amino acid residues in a single polypeptide chain?───一含682個(gè)氨基酸殘基的單個(gè)多肽鏈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基因長(cháng)906 bp,編碼301個(gè)氨基酸。

9 、Based on the findings, the technology for walnut polypeptide wine was probed.───在此基礎上進(jìn)行了核桃多肽酒工藝的研究。

10 、ACTH (adrenocorticotropic hormone)Polypeptide hormone made in the pituitary gland.───促腎上腺皮質(zhì)激素:腦下垂體生成的調節腎上腺皮質(zhì)活性的一種多勝激素。

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種氨基酸、蛋白質(zhì)和多肽。

12 、The recent advances about the action of polypeptide growth factors on apoptosis and interstitial fibrosis in obstructive nephropathy are reviewed.───就近年來(lái)多肽生長(cháng)因子在梗阻腎細胞凋亡、間質(zhì)纖維化中起作用的研究進(jìn)展作一綜述.

13 、Gelatin is soluble polypeptide macromolecule in warm water,and has some kinds of necessary amino acids.───明膠是溫水可溶的多肽高分子聚合物,含有人體所必需的多種氨基酸;

14 、To specify the genetic code for an amino acid or a polypeptide.───指定遺傳密碼確定氨基酸或多肽的遺傳密碼

15 、The invention relates to a nucleic acid controlling the expression of a useful polypeptide, particularly in the posterior silk glands of Bombyx mori .───本發(fā)明涉及指導目的蛋白質(zhì)在家蠶后產(chǎn)絲腺細胞內特異表達的核酸。

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.───方法提高建立大鼠腦損傷模型,用RIA方法測定血漿及腎組織勻漿中垂體腺苷酸環(huán)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.───應用十二烷基磺酸鈉聚丙烯酰胺(SDS-PAGE)凝膠電泳分析香菇菌絲蛋白質(zhì),根據能否檢出22 000道爾頓的34nm香菇病毒外殼蛋白帶作為菌株是否帶病毒的指標。

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...───人胰島淀粉樣多肽（IAPP）試劑盒；

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.───從人LAK細胞酸溶性提取物中純化出一多肽 ,Tricine SDS PAGE表觀(guān)Mr 為 17× 10 3,命名為HLP **2 1(humanlymphocytepeptide) ,具有抗致病性大腸桿菌ML 35P及銅綠假單胞菌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.───它總共約有67%的螺旋結構，還含有少量的轉角結構和松散的多肽鏈。

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.───含有人參皂苷、活性多肽蛋白、深層保濕因子、植物鞣質(zhì)膜，覆蓋肌膚表層，源源釋放養分與抗自由基。

23 、Phage display random peptide library is a kind of polypeptide library developed by filamentous bacteriophages.───摘要噬菌體隨機展示肽庫是一類(lèi)利用絲狀噬菌體發(fā)展起來(lái)的多肽文庫。

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作為分子伴侶在協(xié)助新生多肽鏈折疊,蛋白質(zhì)復合體的裝配,以及調節、修護和降解變性的蛋白質(zhì)方面起著(zhù)重要作用。

26 、The polypeptide compositions of thylakoid membrane were different not in some composition but in some content.───兩優(yōu)培九的類(lèi)囊體膜并不是某些多肽組分存在差異，而是含量差異。

27 、Ru Zhen is comprised of bioactive protein and polypeptide which is extracted from colostrum.───乳珍是從母牛的初乳中提煉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.───序列分析結果表明,獲得的廣西黃雞Gal-4基因大小為321 bp,推導的Gal-4由63個(gè)氨基酸組成,其中N端20個(gè)氨基酸為信號肽,C端38個(gè)氨基酸組成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.───多肽生長(cháng)因子對PDLC功能影響的研究成為牙周組織再生研究的熱點(diǎn)之一。

30 、This course focuses on the mechanisms by which the amino acid sequence of polypeptide chains (proteins), determine their three-dimensional conformation.───本門(mén)課程著(zhù)重在多肽（蛋白質(zhì)）的氨基酸序列如何決定它的三維空間構型的機制。

31 、The peanut is one of the main economic crops and peanut polypeptide has vital physiological function.───摘要花生是我國主要的經(jīng)濟作物之一，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.───多肽實(shí)驗室集團提供品種齊全的縮氨酸，可用于生物和藥物研究。

33 、The anti-fatigue effect of low molecular weight level polypeptide of sea cucumber on mice was studied through different dose lavage.───摘要不同濃度的低分子量海參肽對小鼠灌胃，研究了海參肽對小鼠的抗疲勞作用。

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.───將這三個(gè)組分用反向高效液相色譜技術(shù)進(jìn)一步分離純化，瓊脂糖彌散法篩選純化各組分的抗菌活性，較強抗菌活性的組分進(jìn)行Tricine-SDS-PAGE電泳初步測定分子量及純度。

35 、Glycoprotein is a kind of vital physicological active object, which is made from many covalent forms of polypeptide and oligosccharide.───摘要糖蛋白是由糖鏈與多肽鏈以多種形式共價(jià)修飾而形成的一類(lèi)重要生理活性物質(zhì)。

36 、Polypeptide A compound that contains many amino acids linked together by peptide bonds.───多肽：包含許多由肽鍵連接的氨基酸構成的化合物。

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.───一種叫做釋放因子的蛋白質(zhì)直接結合在終止密碼子上，導致一個(gè)水分子而不是氨基酸被加在肽鏈末端。

38 、The molecular component of a collagen fiber,consisting of three polypeptide chains coiled around each other.───原膠原(蛋白)膠原纖維之組成分子，由三條互相盤(pán)繞在一起的多肽鏈組成

39 、Any of various red, often toxic, polypeptide antibiotics obtained from soil bacteria.───放線(xiàn)菌素一種從土壤細菌中提取的紅色的，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.───并討論了蛋白質(zhì)肽鏈和溶劑環(huán)境對肽段二級結構的調制作用。

41 、Active forms of Fuman EPF is mainly polypeptide of 21.2 KD and 26.3 KD.───早孕血清中EPF的活性形式主要為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質(zhì)有泡沫蛋白和多肽、異葎草酮、類(lèi)黑素、金屬離子、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.───一種多肽用來(lái)（和其他的藥物一起）治療肺結核疾病的多肽抗生素（商標是紫霉素）。

44 、The primary structure is concerned with the number and type of amino acids present and their sequence in the polypeptide chain.───初級結構與氨基酸數量和類(lèi)型,以及它們在多肽鏈上的排列次序有關(guān)。

45 、The initiation codon represents the first amino acid, N-formyl methionine, at the N terminus of the polypeptide.───即編碼多肽N-端第一個(gè)氨基酸即甲硫氨酸（N-甲酸化的）的密碼子。

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).───方法采用高效毛細管電泳法(HPCE)對梔子及其偽品水梔子蛋白多肽進(jìn)行分析。

47 、Trefoil factor 1(TFF1), a member of the trefoil factor family, is a growth factor like small polypeptide.───三葉因子1(TFF1)屬三葉因子家族,是近年來(lái)被人們注意到的具有胃腸道粘膜保護及修復作用的生長(cháng)因子類(lèi)小分子多肽物質(zhì)。

48 、Basic single-chain polypeptide that inhibits numerous serine proteases by binding to the active site of the enzyme, form ing tight complexes.───基本的單鏈多肽，通過(guò)與酶的活性位點(diǎn)緊密結合形成復合物，抑制大多數的絲氨酸蛋白酶。

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、鳥(niǎo)甘酸、肌苷酸及多肽和氨基酸等美味物質(zhì)異常豐富，還含有大量的維生素B群。

50 、This product is made of the mixture of polynucieotide,aminoacid and polypeptide whose molecular weight is lower than 5000 Dalton.───本品系用健康豬脾或牛脾為原料，經(jīng)細胞破碎超濾等工藝步驟提取的分子量小于5000道爾頓的多肽，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.───對分離的基因來(lái)說(shuō)，它可被定義成一組需要用來(lái)產(chǎn)生蛋白質(zhì)的脫氧核糖核酸序列，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.───其所需的氣體控制系統比接觸式密封的油系統要簡(jiǎn)單得多。

53 、The ORF encoding p10 was 261 nucleotide long and encoding a putative 87 amino acid polypeptide of 9.3 kD.───P10基因編碼區全長(cháng)261bp，可編碼分子量為9.3kD，由87個(gè)氨基酸殘基組成的多肽。

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藝條件,并對制得的富含多肽的水解液的脫苦、脫腥及沉淀等問(wèn)題進(jìn)行了探討。

55 、Endothelin is a kind of polypeptide generated by vascular endothelial cells and smooth muscle cells.───內皮素是一族由血管內皮細胞和平滑肌細胞產(chǎn)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.───桿菌肽素：一種從菌系（模式種）中獲得的多肽抗菌素，在對某種細菌傳染病的治療，尤指那些由球菌引起的傳染病的治療中用作局部軟膏

57 、Ingredient: Collagen Protein, Ginkgo Extract, L-vitamin C, Biological Whitening Polypeptide, Lytic Keratinase, CY1100, Aquaxyl, Lactic Acid.───主要成份：膠原蛋白、銀杏精華、左旋維生素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.───中國深圳專(zhuān)業(yè)從事多肽系列產(chǎn)品研究、開(kāi)發(fā)和生產(chǎn)的高新技術(shù)企業(yè)。

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;類(lèi)**脂聚合物;兩相酶膜反應器

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.───枯草桿菌素一種從菌系（枯草芽孢桿菌屬）中獲得的多肽抗菌素，在對某種細菌傳染病，尤指那些由球菌引起的傳染病的治療中用作局部軟膏

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 最初在神經(jīng)組織中提取的多肽，它能起到傳導信息，調控細胞生長(cháng)的作用，它的丟失有可能使細胞的生長(cháng)失控，與腫瘤**轉移密切相關(guān)。

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.───本工作發(fā)現,腹腔注射牛胰多肽可以減輕半胱胺引起的大鼠十二指腸潰瘍,還可防止半胱胺引起的大鼠十二指腸粘膜生長(cháng)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.───植物的耐性機制表現在耐重金屬生態(tài)型的產(chǎn)生、重金屬結合多肽的形成、重金屬離子的區域化以及活性氧自由基清除系統的活化.

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.───乳鏈菌肽是某些乳鏈球菌產(chǎn)生的一種多肽物質(zhì),對引起食品腐敗的大多數革蘭氏**菌有很好的抑制作用,是一種高效、無(wú)毒副作用的天然生物防腐劑。

65 、The polypeptide chain forms a helix with 3.6 amino acid residues per turn and a pitch of 0.54nm.───多肽鏈上每轉3.6個(gè)氨基酸殘基形成一個(gè)螺旋,螺距為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.───一些蛋白質(zhì)不只是由一個(gè)多肽鏈組成的,并且這些蛋白質(zhì)亞基的結構產(chǎn)生了四級結構的。

67 、FGFR3, a member of polypeptide growth factor family, is a tyrosine kinase receptor.───FGFR3是這一多肽類(lèi)生長(cháng)因子的家族成員之一，它是一種酪氨酸激酶受體。

68 、The anti-fatigue effects of sea encumber polypeptide on mice was studied at different dose.───摘要通過(guò)采用不同濃度的海參肽灌胃，研究海參肽對小鼠的抗疲勞作用。

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質(zhì)為雜醇類(lèi)、醛類(lèi)、酚類(lèi)化合物、含硫化合物、生物堿、多肽、氨基酸、無(wú)機盆。

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.───多肽組分別用花生多肽水溶液灌胃(400、800mg/kgbw),實(shí)驗周期32d。

71 、Gelatin is soluble polypeptide macromolecule in warm water, and has some kinds of necessary amino acids.───明膠是溫水可溶的多肽高分子聚合物，含有人體所必需的多種氨基酸；

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獲得其全長(cháng)。該基因cDNA全長(cháng)為1943 bp，開(kāi)放閱讀框含1218 bp，編碼406個(gè)氨基酸，預測分子量為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.───枯草桿菌素，一種從菌系（枯草芽孢桿菌屬）中獲得的多肽抗菌素，在對某種細菌傳染病，尤指那些由球菌引起的傳染病的治療中用作局部軟膏。

74 、The candidate protein was identified as CTGF,a member of CCN polypeptide super-family.───所獲取的候選蛋白為CTGF,是CCN多肽家族成員。

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.───對Holotrichia diomphalia Bates(蠐螬)的水浸液、乙醇提取液、石油醚提取液進(jìn)行了成分分析,結果表明蠐螬中含有氨基酸、多肽或蛋白質(zhì)、糖類(lèi)、生物堿、有機酸鹽、甾體化合物等成分。

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.───大鼠腦外傷組血漿垂體腺苷酸環(huán)化酶激活肽含量明顯高于對照組,而腎組織勻漿中垂體腺苷酸環(huán)化酶激活肽含量明顯低于對照組。

77 、The molecular component of a collagen fiber, consisting of three polypeptide chains coiled around each other.───原膠原（蛋白）膠原纖維之組成分子，由三條互相盤(pán)繞在一起的多肽鏈組成

78 、The s271 homolog isolated was a partial cDNA sequence and also encoded a polypeptide homologous to an Arabidopsis protein.───5271的同源序列的編碼區不完整，所編碼的多膚與擬南芥一個(gè)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%.───在此條件下對鹿**進(jìn)行水解，水解度達34.5%，多肽得率達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.───文章主要介紹了抗原展示系統和多肽表達系統，并分別列舉一些植物病毒作為表達載體的研究進(jìn)展情況以及應用前景。

81 、These results revealed that STFC was a polypeptide with M.W. of 12,870 dalton.───實(shí)驗結果表明,TF_(HSV-1)特異成分是12,870 dalton的多肽。

trna如何決定其功能？

tRNA為T(mén)ransfer_RNA的簡(jiǎn)稱(chēng)，又稱(chēng)轉運RNA、轉移RNA，是小RNA分子，能夠在轉譯時(shí)，攜帶特定的氨基酸到正再加上氨基酸的多肽鏈(polypeptide chain)的ribosomal site上。 擴展資料

tRNA能認得特定的密碼子，有個(gè)能使氨基酸接附在其上的位置。藉由反密碼子使得每個(gè)tRNA能辨識的密碼子均不同。（反密碼子包含一段與mRNA上一段互補的序列）每個(gè)tRNA分子理論上只能與一種氨基酸接附，但是遺傳密碼有簡(jiǎn)并性（degenerate），使得有多于一個(gè)以上的tRNA可以跟一種氨基酸接附。 按照Francis Crick的假設，tRNA是一種“適配”分子，介導mRNA序列上密碼子的'識別，并且翻譯成相應的氨基酸。 類(lèi)攜帶激活氨基酸，將它帶到蛋白質(zhì)合成部位并將氨基酸整合到生長(cháng)著(zhù)的肽鏈上的RNA。tRNA含有能識別模板mRNA上互補密碼的反密碼。

它既是運載活化型氨基酸（由胞液至核糖體上），又是識別mRNA分子中密碼子的工具。一種氨基酸?？捎蓴捣N特定的tRNA來(lái)運載，速度較快。tRNA這種功能是由于其特殊的結構所決定的。tRNA 3'端有一共同結構為—C—C—A。在A(yíng)的第三碳原子上的OH基可與活性氨基酸結合。其另一端是反密碼環(huán)，中間有三個(gè)相鄰的核苷酸組成的反密碼子，按堿基互補原則去辨認mRNA分子的密碼子位置，從而保證了各種氨基酸準確無(wú)誤的按順序進(jìn)入蛋白質(zhì)肽鏈中去。

農桿菌的背景資料

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.