第八章 真核基因表达调控2.ppt

人a-珠蛋白基因，小鼠a-珠蛋白基因和人y-珠蛋白基因的CpG密度依次降低； 未甲基化3基因都能表达，全部甲基化都不表达； 引入增强子后，全部甲基化的小鼠a-珠蛋白基因和人y-珠蛋白基因能表达； 引入增强子后，部分甲基化的人a-珠蛋白基因表达，全部甲基化后不表达。 A fully methylated site is a palindromic sequence that is methylated on both strands of DNA. Most DNA methylations are found on cytosine on both strands of the CpG doublet. A hemi-methylated site is a palindromic sequence that is methylated on only one strand of DNA. Replication converts a fully methylated site to a hemi-methylated site. A demethylase is a casual name for an enzyme that removes a methyl group, typically from DNA, RNA, or protein. A methyltransferase (Methylase) is an enzyme that adds a methyl group to a substrate, which can be a small molecule, a protein, or a nucleic acid. A de novo methylase adds a methyl group to an unmethylated target sequence on DNA. A maintenance methylase adds a methyl group to a target site that is already hemimethylated. terms 2. 转录水平的调控 * TFIIB recognition element (BRE) The TATA element/box Initiator (Inr) The downstream promoter elements (DPE, DCE) Pol II core promoter RNAPII的核心元件有4种： * 调控元件在调控转录起始时候比启动子核心区更有效 Those increasing transcription: Promoter proximal elements:近启动子区 Upstream activator sequences (UASs)：上游激活区 Enhancers：增强子 Those repressing elements: silencers, boundary elements, insulators (绝缘体) Regulatory sequences 增强子作用机制 影响模板附近的DNA双螺旋结构，导致DNA双螺旋弯折或在反式作用因子的参与下，以蛋白质之间的相互作用为媒介形成增强子与启动子之间的成环结构，激活基因转录； 将模板固定于细胞核内固定位置，有利于拓扑异构酶改变DNA双螺旋，促进RNAPII在DNA上的结合和滑动； 增强子区可以作为反式作用因子或RNAPII进入染色质的入口. 三种真核生物RNAP起始转录的特点 转录起始复合物的形成过程 各种转录因子的作用 Eukaryotes: general transcription factors (GTFs) (sufficient for initiate the transcription by RNA Pol in vitro but not in vivo). TFI factors for RNAP I, TFII factors for RNAP II ， TFIII factors for RNAP III TBP，TAF etc….. polⅡ TFⅡH TAF TFⅡF TAF TAF TFⅡA TFⅡB TBP TATA RNAP I： rRNA转录的起始 RNAPIII RNAP III： tRNA 转录的起始 * TBP in TFIID binds to the TATA box TFIIA and TFIIB are recruited with TFIIB binding to the BRE RNA Pol II-TFIIF complex is the