(整理)第34章DNA的复制和修复

1、精品文档第三十四章 DNA的复制和修复第一节DNA的复制（一）It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.j a miXILAR TTMUCTL NUf LFiC A£l£n精品文档（一）DNA的半保留复制hJ(Ill B 油DNA 半保留复制的实验证据：1958年Meselson和Stahl的实验xyxyz§9

2、（二）DNA复制的起点和方式I'in idilio nulrep I il jitiuii,IJiijhik / bfaelrd（三）DNA聚合反应有关的酶1956年Kornberg发现的DNA 聚合酶I （100kg大肠杆菌可以分离 0.5g纯化的酶），由一 条肽链组成，有5' 一3'聚合酶活力，5' -3'外切酶活力，和3' - 5'外切酶活力。用蛋白酶水解得到的Klenow片段有3' - 5'外切酶活力和5' -3'聚合酶活力。DNA聚合酶催化的反应Pretease cleavageDNA polym

3、erase I has three enzymatic activities in a single polypeptide chain, which can be cleaved into two functional parts by mild protease treatment.图示为K1E0W片段与DNA的结合，模板链（12口t）为苴色.引物钺（14叫为红色DNA 聚合酶I的Klenow 片段与DNA 的相互作用DNA聚合酶I的校对作用IJXApr ih nieruMj 1DNA聚合酶I的5' y3'外切酶可以从单链切口的5'可以用脱氧核甘酸填补缺口。Ndk

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8、tM匹1>)ukietnxHdbf i RMbniriki w*mHini swarnt jnCK>itrin)证工消融utiatm ,m wn w 则liitmf 修-,LDmtiwa*dMEnnim it，m”叽mjae，鼻9 a 2M"|" Ml pEHBlm TtH5id IffUhiEllLDNA聚合酶出的结构ridUHC JS-!<1 EvhdA.尸解-EhtMML 3Kkanml-ijitH'iA poincng Ml. An cnra* idiinBHiii-, cunpcMid ot udainilH- r 1 M III 性 d

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12、;1 m* idr*!i «jmi«nchFl； -J 十卡 r |l|.II, B1由 I 4Uri II I”卜 >ll.-MI$ d= F'- I'- duir华 «1l I-,-I Itk-曰 1d ii才餐1#* mih >jivd ,i fci.，iri / duu>hl« li« I K ii-ghrii km1 rtk* I h*/MbriwiHll 1i- -n '1 4- II ? _ , ! DNA聚合酶出的a亚基二聚体与DNA结合的空间关系 （顶部观）DNA聚合酶出的a亚基二聚体

13、与DNA结合的空间关系（立体图）DNA 聚合酶H有不少于 7个亚基，可能参与 DNA 的修复，1999年发现的DNA 聚合酶IV 和V可以复制有较多损伤的 DNA 。DNA连接酶的作用机制。细菌的DNA连接酶以NAD为能源，动物细胞和噬菌体的连接酶以 ATP为能源。T4的DNA 连接酶可以连接平末端。土.I k j L llk.ia Hull Al(h 呻，1 11I l/lINil iFl illiltllllln141 I iIVIIl lc«i"h'I, f". （四）DNA的半不连续复制从寻找失踪的酶到同位素脉冲标记发现冈崎片断4 >k.i/

14、4ki frawmu riKrrplKaiicin lork第一节DNA的复制（二）（五）DNA复制的拓扑性质拓扑异构酶I可以消除负超螺旋，对正超螺旋无作用。拓扑异构酶H可以在消耗 ATP的条件下连续的引入负超螺旋，在无ATP消耗的条件下，可以松弛负超螺旋。真核生物的拓扑异构酶I可以消除负超螺旋，也可以消除正超螺旋。真核生物的拓扑异构酶n （分为“和3两种）可以消除负超螺旋和正超螺旋，但不能引入负超螺旋。拓扑异构酶I主要和转录有关。拓扑异构酶n主要与复制有关。拓扑异构酶n引入负超螺旋可以消除复制叉前进时带来的扭曲张力。双螺旋的解开需要解螺旋酶参与。DnaB是一种解螺旋酶，沿模板链的 5'

15、; y 3'方向移动，由ATP供能，可能参与复制。解螺旋酶I、n和出沿模板链的5' y3'方向移动，rep蛋白1才3' y 5'方向移动，这几种解螺旋酶可能与修复作用有关。SSB可以稳定单链，与单链的结合有协同效应。TABLE 25-3 Protttni Haqulr«J to Initiate Rfplkatton at Tht f. ocM Ori ginMsuJbwnrsfuncbQfDnM ptotert52,0001fl>K|nto» M sequence: open dgn at 9Pte微 s*» ino

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17、inds sn0Han加d PNAANA pd刑"的e畤 4,0005Facilirstes Dn3A aaiwiyDUA 即 mc (EMA w' :的烟- M)400.00。4Hei mu ttnloMd 0r的 tented by DW urwh(><Dtli Hketlidtr3Z.0D01MriJryidtes, 15')GATC rfqUdlurdt LVTV飞Uhi.hb h BHW CHfh itfl Mamins（六）DNA复制的过程复制的起始大肠杆菌DNA复制的步骤H f - iiife | +3,Z iewz.“I大肠杆菌DNA复制时

18、冈崎片段的合成步骤3i * 1 KN X 111 irrT %?ii/l IH， | "i ri in复制的延伸dUlkUlI'lH ij :-H -> - InJ r'-Ci Ei)ta 1<>«1 ijrnttvwv，rwi th，(ril由 t=ZA K unvciuEid by thb 口3_6 IRNA p Eiiu-»r W prr*p.»%k5- 4iau.ki frMHL 吐 口Dhjn 22d knc *£i tnp 5 出 fl Udlrw T»<n/t 2t-14 ON.A

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24、i«s-M F Wl 工 Ml- f*pHf N 5中也由II HH dF LF-fcl db-rl>41 一OnK111J/_ 一dJ “ . Jk/ Ermip0nmp T*Twitnftmr<_£L rfZ* " J1unia 1J MpaiKik*/1 Bh* 由ai（七）真核生物DNA的复制DNA replication in eukaryotic cells use essentially the same principles but being more complex in the details.The best understoo

25、d eukaryotic replication system is that of SV40 and yeast.Formation of the RNA primers and the initial incorporation of deoxynucleotides are believed to be catalyzed by DNA polymerase a (which has no proofreading activity).Later chain extension is believed to be catalyzed by DNA polymerase ? , which

26、 has proofreading activity and is clamped onto the DNA templates via the PCNA trimer rings.Specific sequences (150 bp) that can function as replication origins have only been identified in yeast ( is called autonomously replicating sequences, or ARS) and SV40 virus.The rate of DNA synthesis in eukar

27、yotic cells is about one tenth of that of the E.coli cells. Replication in the eukaryotic genomes begin at many replication origins.9 purified proteins are needed to replicate SV40 virus DNA in vitro.T antigen : a multifunctional site-specific DNA binding protein encoded by SV40 DNA, binds to the or

28、igin(as DnaA) and melts the duplex DNA (as DnaB);RPA : encoded by the host mammalian cells and binds to the melted single-stranded DNA (as SSB).Pol a /primase: synthesizes the RNA primers and a stretch of DNA sequences, has no proofreading activity.Pol ? replaces Pol a /primase to further extend the

29、 RNA-DNA strand, has proofreading activity. PCNA (proliferating cell nuclear antigen) : a trimeric ring-shaped protein that clamps Pol ? onto the DNA emplate.RFC (replication factor C) : a clamp loader for PCNA.Topoisomerases Relieves the torsional strain induced by the growing replication fork.Liga

30、ses： joins the Okazaki fragments (which is much shorter than those in E.coli cells), as well as the leading strand.几种真核细胞的DNA聚合酶的性质如表中所示， 体外或者是体内的实验均证明，DNA聚合酶a和8可以被抑制剂2/3/ -双脱氧胸背和助肠霉素抑制， 这些结果可以说明它们是 DNA 的复制酶。Table 15.2 There are 5 marnmal'an DNA glymerase/ i RcnM%。M Greek teller ye&mi equ*vd

31、ilents are giver Roman nurners)DNA Polymerasen（i）MIH)r (|1)LocationNudearNuclear附皿阳NudearMrCQChandr%alSynifwrc fuFcfiPrimingDMA synthasisReparrRepairR明gtmOther kiHdidn-3-5'+mnud电电钝31-3'杵*3'-Sh ewonudeasflInhiMofSapiiidicotinaptiidfcclinaphid tcol indideaxy-TTPdk>eQKY-TTPDNA聚合酶a主要是用来起始

32、链的合成，而 DNA聚合酶8则是用来延伸新生成的链的。另外两种DNA聚合酶e和3 ,则主要是用来参与修复反应的。而 DNA聚合酶丫则是负责 线粒体DNA的复制的。原核和真核生物复制体系的比较E.coliXDnaAoDnaBDnaBDnaCPDnaGDnaGSV40/AT抗原T抗原Pd 引发醵酵母ORCMCMCdc6Pola 引发Bl功能起始蛋白 解掩酷 装配因子 引发酣P4W的口亚基 p&ni的e亚基 PoHII的6亚基 y复合体 SSB校正滑动钳滑动钳装配器单槌堵合蛋白Pol 5Pal 8 J?ol ePol 5Pol 5 ePCNA(增殖核抗原)PCNARF-CRF-CRF-ARF

33、-AModel of in vitro replication of SV40 DNA by eukaryotic enzymes:1. T antigen (Tag) binds and unwinds replication origin;2. RPA (or RFA) binds to single-stranded DNA;3. Pol a -primase synthesizes the primers (RNA + DNA).Leading strandend of leadingPrimerSV4O DNABinding of at originInitiationRPAForm

34、ation of prepriming complexUnwinding of duplex and binding of RPA to unwound template strarda* .Binding of " Hiisa-Pol a Primer synthesis by pri mese Sin ding of RFC口NAv力总in synthesis by Pol a stimulated bry RFC什- SV40 Origin hS| it iritiliaiF14. RFC loads PCNA to the template.5. PCNA displaces

35、 Pol a -primase and functions as a DNA clamp;6. Pol ? replaces Pol -primase and further extends the DNA strands.PCNAOkazakiLeading fragment / strand(lagging strandj酵母的自主复制区多个 ARS (autonomously replicationg sequence)发挥复制起点的功能。酵母染色体IV的着丝粒附近为ARS1序列，ARS1分为A,B,C三个功能区，A,B起主要作用，C起次要作用。A区为15bp,其中11个保守，称ACS

36、(ARS consensus sequence)。有复 制起始子的功能。 B区约为80bp,含B1,B2,B3 三个功能区。B3是ABF1 ( ARS-binding factor 1)结合区。ORC (origin recognizing complex):由6个亚基组成相当于 DnaA 和入的O 蛋白，与A/B1 结 合后结合于游离的DNA 。Continued leading- and laggtng-strand synthesisLaggingstrand/，Pol a zBinding of Pol 5 to PCNA-RFC complex and synthesis of le

37、ading strandsBinding of primase- Pol a and RFC to tagging-strand template and synthesis of lagging strands discontinuouslyJPol aInterruption of leading-strand synthesisBinding of PCNA displaces primase-Pol aCdc6:相当于DnaC,及入的P蛋白，使Mcm 蛋白结合到复合体上。 这对于在Origin上起始复 制是必须的。Mcm: DnaB 螺旋酶。即 licensing factor.ABF

38、1 :(转录因子)结合于 B3.酵母DNA复制的起始周期蛋白-周用蛋白 依赖性蛋白激曲由薛母北汇曲国基因编 袒的另一种蛋白激.醋前襄制复廿体J nxC«l4 7-tIhtf <MtC，tc1钻电体推持赛白（复期许可因子后复制复合怦< . mrt|1PCNA （增殖细胞核抗原）三聚体的结构与原核生物DNA聚合酶出 的3亚基二聚体相似。I | - L F 0 ”I -1b !T H !' II V WW TF- 1! LIB!-> -1» ,S -= H 111! = TF! 一fb|真核生物DNA复制的模式（b）当加tt聚合能接近下游冈崎片段的RH喝

39、f物时，KWase Hl降 解LN腐附到弟后一t愧昔魏，侵后一个楂音阻由同1片加切 除.连哼酶隹播两一忖司崎片型断.-'前导游的制或由UKA笨号翦口起血然后RK除 去Dt成台明给台FOT斓DW&E合前6 （图中大 示出），滞后廉的甘咸由州；瞿含醉。起蛤合成引 物.蕉后由阪装装pc鼬和口川屐a的（$e）.应.同照片段.以下图示（a）为滞后链末端的引物被切除后会形成缺口，图示（b）为端粒酶可以加长 DNA的末端。IjNA phmcrsArPriiTiri'*dpJ elrj：rtiwaw0.,A IT C(A AAM1L 牝L AA.AltaiI，ila.'il .

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43、 I ： rruh r We "WM»em> hNA- Ulnillmr m.ehIWIaidntr-a第二节DNA的损伤修复（一）错配修复大肠杆菌的Dam甲基化酶可以使DNA的GATC序列中A的N6甲基化，新合成的链在短 期内未能甲基化，如果有错配碱基对，则需切除新合成链的错配区，MutS二聚体识别并结合到错配碱基部位，mutL二聚体与MutS结合，使DNA形成突环，复合体随 ATP水解而移动，直至遇到GATC序列，随后核酸内切酶 MutH 结合到MutSL上，将未甲基化链GATC 位点G的5'端切开，若切开处位于错配碱基的 3'侧，则由核酸外切酶I

44、或核酸外切酶 X ?占3' 一 5'方向切除核酸链。若切开处位于错配碱基的5'侧，则由核酸外切酶口或 RecJ 1g5'- 3'方向切除核酸链，新的DNA链由DNA聚合酶出和连接酶合成并连接。在切除链的过程中，解螺旋酶H和SSB帮助链的解开。人类的hMSH2和hMLHI基因编码的蛋白质分别与大肠杆菌的MutS和MutL相对应，错配修复的过程与大肠杆菌相似。FIGURE 2520 Met halation jnd mismifch repar. Methybtion ot DNA slrarKk can serve Lo dkttrguhh parent

45、itemplale) ftranck from newly syntlwriatBd rtranck in E cot DN儿 a function ihat is trit我鼾 k mjsmab h repairFig 2521), The methylE3n egj序 al ifw N；ofmd01nBi in (5*KjATC cm|umkk. Thisk a palindrome (F|g. 3-2Q* pmeftt in cppotile oriMationt on th« two strands.iFsr 地-itii «rttolllMU-iry7Ktim.t

46、he Ui mphitj0 vFtT£i nd i* n、4hvLdikec m nd <1>« ii&w ntrtaiclmjit.AflQlT H f>” ElE.tE the new atrtind us AiiL-l liylditL4J h nd tl 中 wm 岫 |储cftn m” lonr11iLi 1511TcviupLexA')?+*AMutH de jve thtnnindifiK'd 加口口仃CHa叫A_VFIGURE 25-21 A model for the earl flep% of mediyi-dt

47、rrcted ml match rapair The pfoteim invoked R diis proem in £. coJ htw been purified Table 25-5) Recngnition of the sequence (55小TC wid 川 ibi mismati h me 耳 r 31底1 fun，U<M必 ot th* MuiH dn<l MutS tejn$r respectively Ihe Mu IL pfdteih orms a compJex with Mu IS at misrridtc h. W A is ihgMml t

48、hr，n曲 h* COfTflln EUch tiwt dw oompleK moves 5imult3n?ousk in b，th di rec liens akog (he DMA unlil it encounftm a MutH protein bound at a Semi methylated CMC $4 qucnce. MutH :leaves the unmetfiylated 驯rand on ihe 5* side c4 the G in thi« sequent«. A corrfJex consislirg di DNA helicase H on

49、d one ot several exonucleases then degrades lh« uimethylated DMA strand from that point towtd ihe mismairh (短电 Fig. 2s_221切开处位 干错配诫的5恻ATPADt'+P,M.： M切开处位午错配网二基的3例F1GUEL 25-il Cmpkting mefh.hiimlT ttonmAkh rqkUr r «Hvhvwri MMOT d DHVlwk4 同 $或看M ofW fif kwMWdttWMB uiwr4 in MW 瞰1川讨 bdwf&l

50、t;品 rik* Mtftl CIBIIflM"tllv- pDirt int bcmd % mfiirulrh- Itp noipEllaw（二）直接修复胸腺喀咤二聚体的形成twl is 6M dptndi m M k> jtlcn -.i tv -； k-Jvai Mk' MjCjw 加 fRMMhli Hw iwvukimg j|p h MW .* DH pulfWiBw I i11- i ! -! I 1 1. 'tJ 'g w ds1Mh（Ib Miiikl i iHK从单细胞生物到鸟类都存在光复活酶，但高等哺乳动物却没有光复活酶，其胸腺喀咤二

51、聚体需要通过切除才能修复。（三）切除修复FIGURE 25-24 NucUdzxciJM rrpair in J&i and humans lh*【附廿 pathway of nucleotide-excjsion repair K sjrnilar in all or雯nisms. An exctnuclease binds to DNA al the site “ a bulky lion and ckaww 由总 damaged DNAqcnd on either 4d电 W N 3km. The DNA-d 13 nuclecdds (13 m«r? or 29 nu

52、cleotide Q9 merls removed with the aid o(a helkase. The gap is filled in ty DNA polymerase, and the remaining nkk 临 with DMA liga蕤(四)重组修复FIGURE 25-37 Models for rccombinitional DNA rcpjjf of stalled mpl" a tk，n 卜，山、Il “ I* -Id c*l|- 41 fade collapses on encountecing a DNA lesion (left) or stran

53、d break righU- Rtcornl »inaiion enzymes pro ni-jtv iIvj DNA "and t阳nUs needed to repair the branched DNA struct or- al rhe replic<MJon fork. A ktion m a single strand 甲 p is repaired in a !/<1- ti<in r9ejuiti昭 the Racf; RtcO, and ItecR pfi t»-ins DculJc-sirond breaks af repai

54、red in a pathway requiring the Rec BCD inziTiw： Bcdhreiiuir Re匚A. RucJmbirtilinnreIhy odditicmH,二nzynvM , g . RwA. RuvB. and RuyC,which process Holliday inlerniediates). Lesions in double-stranded DNA wre repaired by nudertide-exc»sionepdir or other pmlhw那. The replication fork re-forms with the aid of enzymes catalyzing origm-ind«p»nchnt replication wtart, and chromosomal replicati