RNA的生物合成幻灯片.pptVIP

真核生物启动子的多元性 启动子包括 TATA序列(TATA box)：-25 ? -35 TATA box的作用：使转录精确地起始； 增强子、及其对转录的影响 a 增强子是指能使和它连锁的基因转录频率明显增加的DNA序列； b 增强效应十分明显，一般能使基因转录频率增加10-200倍； c 增强效应与其位子和取向无关； 几种常见的DNA结合蛋白的结构 The underlying molecular mechanism of gene silencing provides us with short interfering RNAs (siRNAs) which allows to target any gene with high specificity and efficiency. What is RNA interference (RNAi) What is the outcome, indeed ? Introduction into cells of a double-stranded RNA corresponding to an expressed gene leads to down-regulation of that gene through degradation of its mRNA How does the siRNA work ? Introduction of synthetic small double-strand oligonucleotide (21-23 nt length) corresponding to specific gene into cell will specifically knock down corresponding mRNA in the cell An enzyme complex (Dicer), was discovered in Drosophila (Bernstein et al., 2001) as part of a conserved Dicer family expressed in organisms undergoing RNAi. Dicer contains domains for dsRNA binding, RNA unwinding, and ribonuclease activity, and is associated with additional proteins to drive the cleavage of dsRNA in an ATPdependent manner. The resulting siRNA as part of a multiprotein RNA-inducing silencing complex (RISC) is targeted to the complementary RNA species which is then cleaved. siRNA: Small interfering RNA 真核基因转录的蛋白因子 为蛋白质编码的基因的准确转录受多种转录因子的调控。RNA聚合酶必须在特定的转录因子的参与下才能起始转录。 至今有20种以上蛋白因子参与转录起始，可分为三类： 通用(基础)转录因子(basal transcriptional activity)： 包括TF II A、TF II B、 TF II D、 TF II E、TF II F、TF II H、TF II J等。这些蛋白因子对于准确转录起始是必需的。 三. 真核生物转录 5.转录因子 2. 启动子特异性转录激活蛋白 (promoter-specific transcriptional activators) 它们通过与启动了附近或远离启动子的DNA分子上调控区(增强子)相结合，作用于转录起始复合体组装过程，具有DNA结合域和激活转录所需要的激活结构域。 一般情况，细胞中通用转录因子的种类同基因转录的调控蛋白因子(包括转录激活蛋白、辅助激活蛋白、负调控蛋白因子等)相比，数量较少，但在细胞中的含量是丰富的； 这些通用转录因子在启动子区同RNA聚合酶一起组装成转录起始复合物; 特异性调控蛋白因子种类繁多，但含量即非常之少，它们通过其DNA结合域识别特定的DNA序列，这种特性决定了特异性开或关。 Specific Trans-factor characteristics l? 多为变构蛋白，具有两个功能结构域（domain） DNA-binding domain activat