Alternativesigmascontrol phagedevelopmentEarlyphagepromotersare recognized byXX例：bacterial holoenzymeEarlygene28codesfor a newsigma factorthatdisplacesbacterialsigma噬菌体SP01基因的转录由两个连Middlegp28-core enzymetranscribes phageXmiddlegenes续的α因子替换Middle genes 33and 34code for proteinsthatreplacegp28而控制其改变转Late录起始的专一性gp33-gp34-coreenzymetranscribes phagelate geneswivintuallextwww.ergito.comXFigure 9.40 Transcriptionof phage SPOl genes iscontrolledby two successive substitutions of the sigma factor that changethe initiation specificity
例： 噬菌体SPO1基因 的转录由两个连 续的σ因子替换 而控制其改变转 录起始的专一性
真核生物有三种依赖DNA的RNA聚合酶每一种负责一类基因的转录 RNA polymerase I synthesizes rRNA in the nucleolus.RNA polymerase II synthesizes mRNAinthenucleoplasmRNA polymerase III synthesizes small RNAsinthenucleoplasm: All eukaryotic RNA polymerases have ~12 subunits andare aggregates of >500 kD Some subunits are common to all three RNA polymerases. The largest subunit in RNA polymerase II has a CTD(carboxy-terminal domain)consistingof multiple repeatsof aseptamer
真核生物有三种依赖DNA的RNA聚合酶， 每一种负责一类基因的转录。 · RNA polymerase I synthesizes rRNA in the nucleolus. · RNA polymerase II synthesizes mRNA in the nucleoplasm · RNA polymerase III synthesizes small RNAs in the nucleoplasm. · All eukaryotic RNA polymerases have ~12 subunits and are aggregates of >500 kD. · Some subunits are common to all three RNA polymerases. · The largest subunit in RNA polymerase II has a CTD (carboxy-terminal domain) consisting of multiple repeats of a septamer
RNApolymerasehas>10 subunits真核生物RNA聚合酶kD含有十多种亚基Related to bacterial subunit β200bindsDNAhasCTD=(YSPTSPS)n对原核生物和真核[yeastn=26;mousen=52]Related to bacterial subunitβ生物的RNA聚合酶的100binds nucleotides蛋白质电泳分析表明：50在真核生物中，Relatedto bacterial subunit α一些蛋白质亚基在Commontoall3polymerases所有的RNA聚合酶中25Commontoall3polymerases是共同都具有的。Commontoall3polymerases一些亚基与细菌RNA(@virtualtextwww.ergito.com聚合酶有关系Figure 21.2 Some subunits are common to all classes ofeukaryotic RNA polymerases and some are related to bacterialRNApolymerase
对原核生物和真核 生物的RNA聚合酶的 蛋白质电泳分析表 明： 在真核生物中， 一些蛋白质亚基在 所有的RNA聚合酶中 是共同都具有的。 一些亚基与细菌RNA 聚合酶有关系 真核生物RNA聚合酶 含有十多种亚基
EcalfcoreEukaryoticRNApolvmuraseRNApolymerases(a238)B'and类似β和β'亚基B-like subunits各一个CTDa-like类似α亚基2个subunitsCommon相同的亚基6个subunitsAdditionalenzyme-specific+5酶特有的亚基4subunitsAFIGURE 10-26 Schematicrepresentation ofthe subunit一7个不等structure of yeast nuclearRNA polymerases and comparisonwithE:coli RNAcorepolymerase.All three yeastpolymeraseshave four core subunits that exhibit some homology withthe B.β',and α subunits in E.coti RNApolymerase.Thelargestsubunit(LofRNApolymerase llalso containsan essential C-termi-nal domain(CTD).RNApolymerasesIand Ill containthe sametwo nonidentical c-like subunits,whereaspolymerase llhas twocopies of a different α-like subunit.All threepolymerasessharefive other common subunits (two copies of the largest of these):Inaddition,eachyeastpolymerase containsfourtosevenuniquesmaller subunits
相同的亚基6个 类似α亚基2个 类似β和β’亚基 各一个 酶特有的亚基4 －7个不等
真核生物RNA聚合酶的一般特性酶敏感性功能RNA聚合酶I对α一鹅草碱不敏感转录45SrRNA前体，45SrRNA前体是包含5、8S，18S和28SrRNA基因对放线菌素D敏感的多顺反子单位（I型基因）转录所有编码基因和大多数RNA聚合酶ⅡI为α一鹅蕈碱抑制核内小分子RNAs (Ⅱ 型基因)转录tRNA基因，5SrRNA基因和编码U6mRNA和不同的RNA聚合酶Ⅲ对一α鹅草碱中等敏感scRNAs基因(Ⅲ型基因)
真核生物RNA聚合酶的一般特性 酶 功能 敏感性 RNA聚合酶I RNA聚合酶Ⅱ 为—鹅蕈碱抑制 RNA聚合酶Ⅲ 对—鹅蕈碱中等敏感 对—鹅蕈碱不敏感， 对放线菌素D敏感 转录45SrRNA前体， 45SrRNA前体 是包含 5．8S，18S和28SrRNA基因 的多顺反子单位(I型基因) 转录所有编码基因和大多数 核内小分子RNAs (Ⅱ型基因) 转录tRNA基因，5S rRNA基因 和编码U6 mRNA和不同的 scRNAs基因(Ⅲ型基因)