北京大学生物化学课件15.ppt

二、乳糖操纵子的正性调节 正性调控序列 启动子结构 乳糖操纵子 正性调控 乳糖操纵子 三、乳糖操纵子的协调调节 1、只有正性诱导物 2、同时有正、负性诱导物 3、无正、负性诱导物 4、只有负性诱导物 乳糖操纵子 色氨酸操纵子 色氨酸操纵子 阻遏蛋白结构 色氨酸操纵子的前导序列 色氨酸操纵子 前导序列的配对方式 色氨酸操纵子 色氨酸操纵子的衰减机理 1、Trp浓度高时衰减 2、Trp浓度低时转录 阿拉伯糖操纵子 阿拉伯糖操纵子 噬菌体操纵子 其它操纵子类型 The SOS response in E. coli. The LexA protein is the repressor in this system, with an operator site (indicated in red) near each gene. (a) The recA gene is not entirely repressed by the LexA repressor, and about 1,000 RecA protein monomers are normally found in the cell. (b) When DNA is extensively damaged (e.g., by UV light), DNA replication is halted and the number of single-strand gaps in the DNA increases. (c) RecA protein binds to this single-stranded DNA, activating the proteins coprotease activity. (d) While bound to DNA the RecA protein facilitates the cleavage and inactivation of the LexA repressor. When the repressor is inactivated, the SOS genes, including recA, are induced. RecA protein levels increase 50- to 100-fold SOS反应 SOS反应 细菌鞭毛蛋白重组 A leucine zipper from the yeast activator protein GCN4. The helices are shown in white and light blue. The interacting Leu residues are shown in red and purple. 一、亮氨酸拉链（ Leucine zippers） 闭合拉链 开放拉链 拉链全貌 反式作用因子 亮氨酸拉链 反式作用因子 碱性α螺旋 反式作用因子 锌指结构 反式作用因子 (a) A ribbon representation of a single zinc finger derived from the regulatory protein Zif 268. The zinc atom is in orange and the amino acid residues that coordinate it (two His and two Cys) are shown in red. 锌指结构 (b) Three zinc fingers (light blue and gray) from Zif 268 are shown complexed with DNA. The zinc atoms are again shown in orange. 反式作用因子 真核基因表达调控 (a) Typical eukaryotic transcriptional activators that affect RNA polymerase II. TFIID is a general transcription factor. CTFI, GAL4, and Spl are transcriptional activators that bind to specific DNA sites. PPP: proline-rich; -- : acidic; QQQ: glutamine-rich. Some or all of these proteins may activate transcription via intermediary proteins called coactivators. (b) A chimeric protein with t