转录水平的调控
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•A third possibility is that some combination of both direct and indirect effects might be responsible for activation at individual promoters.
ห้องสมุดไป่ตู้
We can now distinguish 3 classes of CRP-activated promoter:
CLASS I
Class I CRP-activated promoters require only CRP for activation and the CRP binding site is located upstream of the promoter.
The prototype CLASS I CRP-activated promoter is the lac operon promoter (lacP1). This CRP-binding site is centred 61.5 bp upstream of the startpoint of transcription.
翻译过程对转录的调节 衰减作用(弱化作用)
E. Coli 的色氨 酸合成
翻译过程对转录的调节
CLASS III
CLASS III CRP-activated promoters require additional regulator proteins as well as CRP for activation. The location of the CRP binding site can be quite variable though it is typically more than 90 bp upstream of the startpoint of transcription.
OR Does CRP activate transcription indirectly? Since CRP bends and thus distorts the DNA double helix when it binds, is it possible that increased RNA polymerase binding is a result of structural changes in the DNA?
There is no prototype CLASS III CRP-activated promoter since they all have different requirements by way of additional regulator proteins. Examples of CLASS III CRP-activated promoters are the araBAD promoter and the malK promoter
•Does CRP activate transcription directly? In other words, does it assist RNA polymerase to recognize the promoter by means of direct protein-protein contacts between CRP and RNA polymerase?
2.色氨酸操纵子
大肠肝菌培养在只含无机盐及单一 碳源的培养基中，大肠杆菌细胞内可以 测出色氨酸合成的酶系, 如果在培养基 中加入色氨酸, 大肠杆菌中色氨酸合成 的酶系就明显降低。色氨酸存在时, 阻 止了色氨酸合成酶系的形成, 细菌可直 接利用色氨酸, 而不用自己合成, 这种减 少酶量的现象称为酶合成的阻遏。
cAMP-CAP-DNA
Ever since the function of CRP as an activator of transcription was established, a great deal of work has been done to try and understand exactly how this occurs.
CLASS II
CLASS II CRP-activated promoters require only CRP for activation and the CRP binding site overlaps the promoter. In these promoters, the CRP binding site appears to replace the usual -35 region of the promoter.
The prototype CLASS II CRP-activated promoter is the gal operon promoter (galP1). This CRP-binding site is centred 41.5 bp upstream of the startpoint of transcription.
二、转录水平的调控
（一）原核生物的操纵子模型 1.乳糖操纵子
1.乳糖操纵子
大肠杆菌生长需要碳源, 常见的是糖 类, 最方便利用的是葡萄糖, 但有些条件 下培养基中并无葡萄糖，仅有半乳糖等糖 类，这时分解它们的酶类必须合成，才能 利用半乳糖。
当葡萄糖与乳糖共存，情况比
较复杂，分解它们的酶类必须不 合成。
降解物基因活化蛋白CAP（catabolic gene activate protein, CAP), 与cAMP形成 复合物结合于启动子部位，引起DNA构象 的变化，促进RNA聚合酶与启动子结合， 使转录的起始更加频繁，是一种正调控。 当有葡萄糖存在时，其分解代谢产物可抑 制腺苷酸环化酶活性，激活磷酸二酯酶活 性，cAMP含量下降，使CAP失活。
ห้องสมุดไป่ตู้
We can now distinguish 3 classes of CRP-activated promoter:
CLASS I
Class I CRP-activated promoters require only CRP for activation and the CRP binding site is located upstream of the promoter.
The prototype CLASS I CRP-activated promoter is the lac operon promoter (lacP1). This CRP-binding site is centred 61.5 bp upstream of the startpoint of transcription.
翻译过程对转录的调节 衰减作用(弱化作用)
E. Coli 的色氨 酸合成
翻译过程对转录的调节
CLASS III
CLASS III CRP-activated promoters require additional regulator proteins as well as CRP for activation. The location of the CRP binding site can be quite variable though it is typically more than 90 bp upstream of the startpoint of transcription.
OR Does CRP activate transcription indirectly? Since CRP bends and thus distorts the DNA double helix when it binds, is it possible that increased RNA polymerase binding is a result of structural changes in the DNA?
There is no prototype CLASS III CRP-activated promoter since they all have different requirements by way of additional regulator proteins. Examples of CLASS III CRP-activated promoters are the araBAD promoter and the malK promoter
•Does CRP activate transcription directly? In other words, does it assist RNA polymerase to recognize the promoter by means of direct protein-protein contacts between CRP and RNA polymerase?
2.色氨酸操纵子
大肠肝菌培养在只含无机盐及单一 碳源的培养基中，大肠杆菌细胞内可以 测出色氨酸合成的酶系, 如果在培养基 中加入色氨酸, 大肠杆菌中色氨酸合成 的酶系就明显降低。色氨酸存在时, 阻 止了色氨酸合成酶系的形成, 细菌可直 接利用色氨酸, 而不用自己合成, 这种减 少酶量的现象称为酶合成的阻遏。
cAMP-CAP-DNA
Ever since the function of CRP as an activator of transcription was established, a great deal of work has been done to try and understand exactly how this occurs.
CLASS II
CLASS II CRP-activated promoters require only CRP for activation and the CRP binding site overlaps the promoter. In these promoters, the CRP binding site appears to replace the usual -35 region of the promoter.
The prototype CLASS II CRP-activated promoter is the gal operon promoter (galP1). This CRP-binding site is centred 41.5 bp upstream of the startpoint of transcription.
二、转录水平的调控
（一）原核生物的操纵子模型 1.乳糖操纵子
1.乳糖操纵子
大肠杆菌生长需要碳源, 常见的是糖 类, 最方便利用的是葡萄糖, 但有些条件 下培养基中并无葡萄糖，仅有半乳糖等糖 类，这时分解它们的酶类必须合成，才能 利用半乳糖。
当葡萄糖与乳糖共存，情况比
较复杂，分解它们的酶类必须不 合成。
降解物基因活化蛋白CAP（catabolic gene activate protein, CAP), 与cAMP形成 复合物结合于启动子部位，引起DNA构象 的变化，促进RNA聚合酶与启动子结合， 使转录的起始更加频繁，是一种正调控。 当有葡萄糖存在时，其分解代谢产物可抑 制腺苷酸环化酶活性，激活磷酸二酯酶活 性，cAMP含量下降，使CAP失活。