[理學(xué)]第6章原核基因表達(dá)調(diào)控(編輯修改稿)
2025-01-04 01:05 本頁(yè)面
【文章內(nèi)容簡(jiǎn)介】 結(jié)構(gòu)基因的轉(zhuǎn)錄。 Glucose controls expression of lac operon Addition of inducer results in rapid induction of lac mRNA, and is followed after a short lag by synthesis of the enzymes。 removal of inducer is followed by rapid cessation of synthesis. 乳糖操縱子的正調(diào)控 (1) 正調(diào)控位點(diǎn) CRP結(jié)合位點(diǎn) ① 位置 ② 序列特征 (2) 調(diào)節(jié)因子 CRP ① 結(jié)構(gòu)特征 ② 活性控制 (3) CAP與靶位點(diǎn)的作用 The CRP protein can bind at different sites relative to RNA polymerase. CRP結(jié)合位點(diǎn)的位置 CRPbinding sites are close to the promoter 41, one 61, two 92, one The consensus sequence for CRP contains the well conserved pentamer TGTGA and (sometimes) an inversion of this sequence (TCANA). CRP結(jié)合位點(diǎn)序列特征 CRP binds to a consensus sequence ◆ 一個(gè)由兩個(gè)相同亞基組成的二聚體，每個(gè)亞基為 kDa, 二聚體可被單個(gè)分子 cAMP激活。 ◆ CRP單體含一個(gè) DNA結(jié)合區(qū)和一個(gè)轉(zhuǎn)錄激活區(qū)。 CRP的結(jié)構(gòu)特征 Cyclic AMP has a single phosphate group connected to both the 3` and 5` positions of the sugar ring. adenylate cyclase ATP cAMP By reducing the level of cyclic AMP, glucose inhibits the transcription of operons that require CRP activity. The level of cyclic AMP is inversely related to the level of glucose. CRP的活性控制 cAMP Ⅱ AGlc CRP bends DNA 90176。 around the center of symmetry. CRP與靶位點(diǎn)的作用 3 色氨酸操縱子 色氨酸操縱子的結(jié)構(gòu)組成 色氨酸操縱子的調(diào)控模型 trp操縱子的阻遏系統(tǒng) 衰減子對(duì)色氨酸操縱子的表達(dá)調(diào)控 色氨酸操縱子的結(jié)構(gòu)組成 The Trp Operon Note:the order of the genes follows the order of the biosynthetic pathway (1) 輔阻遏蛋白對(duì) trp操縱子表達(dá)的調(diào)控 輔阻遏蛋白（ aporepressor, trpR的產(chǎn)物）通過(guò)與操縱基因的結(jié)合與否來(lái)控制結(jié)構(gòu)基因是否被轉(zhuǎn)錄。 (2) 輔阻遏蛋白的活性控制 輔阻遏蛋白的活性受到色氨酸水平的控制，色氨酸與輔阻遏蛋白結(jié)合則激活了輔阻遏蛋白，這樣輔阻遏蛋白就可與操縱區(qū) DNA結(jié)合，關(guān)閉 trp操縱子的表達(dá)。 trp操縱子的阻遏系統(tǒng) (1) 前導(dǎo)序列和衰減子的序列特征 (2) 色氨酸水平調(diào)控前導(dǎo)區(qū)和衰減子對(duì)應(yīng) RNA二級(jí)結(jié)構(gòu)
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