Dual role for transactivator protein C in activation of mom promoter of bacteriophage Mu
Dual role for transactivator protein C in activation of mom promoter of bacteriophage Mu
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DOI：
10.1074/jbc.m512906200
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发表时间：
2006-03-31
影响因子：
4.8
通讯作者：
Nagaraja, V
中科院分区：
文献类型：
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作者：
Chakraborty, A;Nagaraja, V
噬菌体Mu的反式激活因子C蛋白通过一种不寻常的机制激活噬菌体的mom基因。通过C与其位点的DNA结合导致邻近序列的解旋，重新排列异相启动子元件以促进RNA聚合酶（RNAP）结合。反式激活因子对C非依赖性组成型启动子突变体（其中RNAP已经结合）的高水平刺激表明在RNAP募集后的步骤处的转录激活的另外机制。在这项研究中，我们研究了启动子-聚合酶相互作用的各个步骤，在转录起始过程中使用启动子突变体和C蛋白的阳性对照（PC）突变体。在促进RNAP结合后，反式激活因子不影响开放复合物的形成或其稳定性。然而，在随后的步骤中，该蛋白发挥重要作用，通过增加生产性RNAP来增强启动子清除。启动子复合物反式激活因子C的pc突变体在这一步受到损害，支持C在mom转录激活中的额外下游作用。我们认为，这种不寻常的多步激活P-mom已经发展到确保不可逆的开关在晚期裂解周期的噬菌体。
Transactivator C protein of bacteriophage Mu activates the mom gene of the phage by an unusual mechanism. DNA binding by C to its site results in unwinding of the neighboring sequences, realigning the out- of- phase promoter elements to facilitate RNA polymerase ( RNAP) binding. High level stimulation of a C- independent constitutive promoter mutant ( where RNAP is already bound) by the transactivator suggested an additional mechanism of transcription activation at a step after RNAP recruitment. In this study, we have investigated the various steps of promoter- polymerase interactions during transcription initiation by using both the promoter mutant and a positive control ( pc) mutant of C protein. The transactivator does not influence formation of the open complex or its stability after facilitating the RNAP binding. However, at a subsequent step, the protein exerts an important role, enhancing the promoter clearance by increasing the productive RNAP . promoter complex. The pc mutant of the transactivator C is compromised at this step, supporting the additional downstream role for C in mom transcription activation. We suggest that this unusual multistep activation of P-mom has evolved to ensure irreversibility of the switch during the late lytic cycle of the phage.