MECHANISM OF ACTIVATION OF TRANSCRIPTION INITIATION FROM THE LAMBDA-PRM PROMOTER
MECHANISM OF ACTIVATION OF TRANSCRIPTION INITIATION FROM THE LAMBDA-PRM PROMOTER
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DOI：
10.1016/0022-2836(82)90473-9
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发表时间：
1982-01-01
影响因子：
5.6
通讯作者：
MCCLURE, WR
中科院分区：
文献类型：
--
作者：
HAWLEY, DK;MCCLURE, WR
噬菌体lambda.PRM启动子被lambda.cI基因产物激活的机制。体外实验研究了抑制剂的作用。抑制物的存在增加了在PrM的RNA聚合酶开放复合体的形成速度；启动子的最终占位程度和开放复合体的催化性质不受抑制物的存在的影响。对开放复合体形成的两个步骤的单独定量表明，抑制物特异性地增加了第二步的速率，即封闭的复合体异构化为转录活性的开放复合体。第一步，即RNA聚合酶与启动子的初始结合，形成封闭的复合体，抑制物不会对其产生显著影响。对PrM-35区突变体prmup-1的激活进行了研究，发现其激活机制与野生型启动子相似，尽管在没有阻遏因子的情况下，prmup-1启动子比Prm更频繁地启动。有证据表明，在PrM的RNA聚合酶和OR2的阻遏物之间存在稳定的相互作用，并且阻遏物只需要开放复合体的形成，而不是维持开放复合体的形成。对野生型启动子和prmup-1启动子的体外启动特性的比较表明，突变对开放复合体形成的两个步骤都有影响。PR，x3的A-35突变降低了这两个步骤的有利条件。提出了一个模型，在该模型中，突变只直接影响初始结合的一步，而观察到的对异构化速率的影响是间接的。
The mechanism of activation of the bacteriophage .lambda.PRM promoter by the product of the .lambda.cI gene, the .lambda. repressor, was studied in vitro. Repressor increased the rate of RNA polymerase open complex formation at PRM; the final extent of promoter occupancy and the catalytic properties of the open complexes were unaffected by the presence of repressor. Separate quantitation of the 2 steps of open complex formation showed that repressor specifically enhanced the rate of the 2nd step, the isomerization of the closed complex to the transcriptionally active open complex. The 1st step, the initial binding of the RNA polymerase to the promoter to form the closed complex, was not significantly affected by repressor. The activation of a -35 region mutant of PRM, prmup-1 was studied and the mechanism of activation was found to be analogous to that of the wild-type promoter, even though the prmup-1 promoter initiates more frequently than PRM in the absence of repressor. Evidence for a stabilizing interaction between RNA polymerase at PRM and repressor at OR2 was presented and repressor was demonstrated to be required only for the formation, but not for the maintenance, of the open complex. The comparison of the in vitro initiation properties of the wild-type and prmup-1 promoters revealed an effect of the mutation on both steps of open complex formation. A -35 mutation in PR, x3, decreased the favorability of both steps. A model was proposed in which the mutation directly affects only 1 step, the initial binding, while the observed effect on the isomerization rate is indirect.