Taylor K, Wegrzyn G
Department of Molecular Biology, University of Gdańsk, Poland.
FEMS Microbiol Rev. 1995 Aug;17(1-2):109-19. doi: 10.1111/j.1574-6976.1995.tb00192.x.
A general scheme of lambda phage and plasmid DNA replication in Escherichia coli is presented, and results of in vivo experiments from the authors' laboratory are superimposed. The initiator lambda O functions in the assembly of the replication complex (RC) at ori lambda, making it a stable component of this structure. ClpP/ClpX protease-specific action on lambda O does not affect the regulation of replication; it only degrades the surplus of synthesized lambda O. The initiator lambda O becomes protected from proteolysis at a distinct step of the pathway of RC assembly. The host DnaA initiator-regulated transcriptional activation of ori lambda seems to be coupled with RC assembly at the step of chaperone-mediated rearrangement of the pre-primosome. The once-assembled RC is inherited by one of two lambda plasmid daughter copies at each round of circle-to-circle (theta) replication. The inherited, old RC-driven replication is also dependent on RNA polymerase and DnaA functions. It seems that DnaA licenses lambda plasmid DNA for only one replication round, resembling the putative eukaryotic licensing factor in this respect. The lambda O binding to ori lambda does not seem to play any role in regulation of lambda plasmid replication, and the Cro-autoregulatory loop may be deleted. The emerging picture shows lambda plasmid circles with RCs bound to their ori, awaiting a signal triggering initiation of replication. The host DnaA initiator-regulated transcriptional activation of ori lambda may be involved in signal transmission. Inactivation of DnaA function blocks initiation of lambda phage DNA replication, but the lambdoid prophage Rac compensates this defect and all parental phage DNA molecules, after one round of theta replication switch to the sigma mode and produce progeny in high yield. We suspect that DnaA-regulated transcriptional activation is involved in installation and adequate positioning of two RCs, required for bidirectional replication, but in the Rac-promoted process only one RC may be installed, leading to unidirectional replication continued in the sigma mode. In wild-type cells consumption of DnaA function by the rapidly replicating lambda phage DNA may switch replication from bidirectional theta to unidirectional theta, and later to the sigma mode; the lambda circles produced earlier may play the role of Rac, which is required only when DnaA function has been inactivated prior to phage infection.
本文介绍了λ噬菌体和质粒DNA在大肠杆菌中复制的一般模式，并叠加了作者实验室的体内实验结果。起始因子λO在oriλ处的复制复合体（RC）组装中起作用，使其成为该结构的稳定组成部分。ClpP/ClpX蛋白酶对λO的特异性作用不影响复制调控；它只是降解合成的多余λO。起始因子λO在RC组装途径的一个特定步骤中受到蛋白水解保护。宿主DnaA起始因子调节的oriλ转录激活似乎在伴侣介导的前引发体重排步骤中与RC组装偶联。每次环到环（θ）复制时，组装好的RC会被两个λ质粒子代拷贝之一继承。继承的、由旧RC驱动的复制也依赖于RNA聚合酶和DnaA的功能。似乎DnaA仅许可λ质粒DNA进行一轮复制，在这方面类似于假定的真核许可因子。λO与oriλ的结合似乎在λ质粒复制调控中不起任何作用，并且Cro自调控环可能被删除。新出现的情况是，λ质粒环上结合有RC，等待触发复制起始的信号。宿主DnaA起始因子调节的oriλ转录激活可能参与信号传递。DnaA功能的失活会阻止λ噬菌体DNA复制的起始，但类λ原噬菌体Rac可弥补这一缺陷，并且所有亲代噬菌体DNA分子在一轮θ复制后切换到σ模式并高产产生后代。我们怀疑DnaA调节的转录激活参与双向复制所需的两个RC的安装和适当定位，但在Rac促进的过程中可能只安装一个RC，导致以σ模式继续单向复制。在野生型细胞中，快速复制的λ噬菌体DNA对DnaA功能的消耗可能会使复制从双向θ切换到单向θ，随后切换到σ模式；早期产生的λ环可能起到Rac的作用，仅在噬菌体感染前DnaA功能失活时才需要Rac。
