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首页> 外文期刊>Journal of Molecular Biology >The Mechanism of Transcriptional Activation by the Topologically DNA-linked Sliding Clamp of Bacteriophage T4.
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The Mechanism of Transcriptional Activation by the Topologically DNA-linked Sliding Clamp of Bacteriophage T4.

机译：噬菌体T4的拓扑DNA连接的滑动夹转录激活的机制。

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摘要

Three viral proteins participate directly in transcription of bacteriophage T4 late genes: the sigma-family protein gp55 provides promoter recognition, gp33 is the co-activator, and gp45 is the activator of transcription; gp33 also represses transcription in the absence of gp45. Transcriptional activation by gp45, the toroidal sliding clamp of the T4 DNA polymerase holoenzyme, requires assembly at primer-template junctions by its clamp loader. The mechanism of transcriptional activation has been analyzed by examining rates of formation of open promoter complexes. The basal gp55-RNA polymerase holoenzyme is only weakly held in its initially formed closed promoter complex, which subsequently opens very slowly. Activation ( approximately 320-fold in this work) increases affinity in the closed complex and accelerates promoter opening. Promoter opening by gp55 is also thermo-irreversible: the T4 late promoter does not open at 0 degrees C, but once opened at 30 degrees C remains open upon shift to the lower temperature. At a hybrid promoter for sigma(70) and gp55-holoenzymes, only gp55 confers thermo-irreversibility of promoter opening. Interaction of gp45 with a C-terminal epitope of gp33 is essential for the co-activator function of gp33.
机译：三种病毒蛋白直接参与噬菌体T4晚期基因的转录：σ家族蛋白gp55提供启动子识别，gp33是共激活子，而gp45是转录激活子。在不存在gp45的情况下，gp33还抑制转录。通过gp45（T4 DNA聚合酶全酶的环形滑动夹具）进行转录激活，需要通过其夹具装载器在引物-模板连接处进行组装。已经通过检查开放启动子复合物的形成速率分析了转录激活的机制。基本的gp55-RNA聚合酶全酶仅弱地保留在其最初形成的封闭启动子复合物中，随后其打开非常缓慢。激活（在这项工作中约为320倍）增加了封闭复合物中的亲和力并加速了启动子的开放。 gp55的启动子开启也是热不可逆的：T4晚期启动子在0摄氏度时不会打开，但一旦在30摄氏度时开启，则转移至较低温度后仍会保持开启状态。在sigma（70）和gp55-全酶的混合启动子上，只有gp55赋予启动子开放热不可逆性。 gp45与gp33的C末端表位的相互作用对于gp33的共激活功能至关重要。

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