第八章真核基因表达调控1.pptVIP

核小体是染色质的基本结构单位 Part I: Histone modification If nucleosomes form at a promoter, transcription factors (and RNA polymerase) cannot bind. If transcription factors (and RNA polymerase) bind to the promoter to establish a stable complex for initiation, histones are excluded. The dynamic model for transcription of chromatin relies upon factors that can use energy provided by hydrolysis of ATP to displace nucleosomes from specific DNA sequences. Chromatin remodeling Chromatin remodeling is undertaken by large complexes that use ATP hydrolysis to provide the energy for remodeling. The heart of the remodeling complex is its ATPase subunit. Remodeling complexes are usually classified according to the type of ATPase subunit two major types of chromatin remodeling complex: SWI/SNF and ISW Zinc Finger bHLH bZIP Homeodomain 1） TF最常见的DNA binding domain (1) 锌指(zinc finger) 常结合GC box Cys-X2-4-Cys-X3-Phe-X5-Leu-X2-His-X3-His C-terminal: α-helix ?binding DNA Cys-X2-Cys-X13-Cys-X2-Cys 碱性亮氨酸拉链（bZIP: basic Leu Zip)结构域转录激活因子序列比较 (2) 碱性亮氨酸拉链 bZIP bHLH蛋白(basic Helix-Loop-Helix) (3) 碱性螺旋-环-螺旋bHLH 2） TF常见的trans-activation domain (Activation domain is interchangeable) Interaction Assays Design of Two-hybrid / Three-hybrid /etc… separable functional domains Two-hybrid assay (protein-protein) Tri-hybrid assay (protein-RNA) 1. RNA polymerase II2. promoter and enhancers3. transcription factors Eukaryotic gene expression is usually controlled at the level of initiation of transcription. 真核基因转录起始的调控 Ordered Assembly and Pol II Holoenzyme TFIID TFIID one-step multiple-step TFIIB binds to DNA and contacts RNA polymerase near the RNA exit site and at the active center, and orients it on DNA. +25bp Sequential Assembly TBP: TATA binding protein TAFs: TBP associated factors Binding of TFIID (TBP + 11 TAFs, 800KD) to the TATA box is the first step in initiation. Phosphorylation of the CTD by the kinase activity of TFIIH may be needed to release RNA polymerase to start transcription. · TFIIE and