Bacteriophage T4 gene 41 helicase and gene 59 helicase-loading protein: A versatile couple with roles in replication and recombination
Bacteriophage T4 gene 41 helicase and gene 59 helicase-loading protein: A versatile couple with roles in replication and recombination
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DOI：
10.1073/pnas.121009398
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发表时间：
2001-07-17
影响因子：
11.1
通讯作者：
Nossal, NG
中科院分区：
文献类型：
--
作者：
Jones, CE;Mueser, TC;Nossal, NG
噬菌体T4使用两种复制起始模式：感染早期的起点依赖性复制和后期的重组依赖性复制。相同的相对简单的T4复制蛋白复合物负责两种DNA合成模式。因此，用于装载T4 41解旋酶的机制必须足够通用，以允许其装载在通过在几个起点处转录产生的9个环上、通过重组产生的D环上以及停滞的复制叉上。T4 59解旋酶加载蛋白是一种小的、碱性的、几乎完全α-螺旋的蛋白，其N-末端结构域与高迁移率族家族蛋白具有结构相似性。在本文中，我们回顾了最近的证据，59蛋白识别特定的结构，而不是特定的序列。它结合并加载复制叉和三链和四链（霍利迪连接）重组结构上的解旋酶，没有序列特异性。我们总结了我们的实验表明，纯化的T4酶催化完整的单向复制的质粒含有T4 ori（uvsY）的起点，与预先形成的9环的位置9环确定在这个起点在体内。这种复制依赖于41解旋酶，并受到59蛋白的强烈刺激。此外，解旋酶加载蛋白通过阻断ori（uvsY）R环质粒上的复制直到解旋酶被加载来帮助协调前导链和滞后链的合成。T4酶也可以复制具有9个环的质粒，这些环不具有T4起始序列，但仅当9个环在容易解绕的DNA序列内时。
Bacteriophage T4 uses two modes of replication initiation: origin-dependent replication early in infection and recombination-dependent replication at later times. The same relatively simple complex of T4 replication proteins is responsible for both modes of DNA synthesis. Thus the mechanism for loading the T4 41 helicase must be versatile enough to allow it to be loaded on 9 loops created by transcription at several origins, on D loops created by recombination, and on stalled replication forks. T4 59 helicase-loading protein is a small, basic, almost completely alpha -helical protein whose N-terminal domain has structural similarity to high mobility group family proteins. In this paper we review recent evidence that 59 protein recognizes specific structures rather than specific sequences. It binds and loads the helicase on replication forks and on three- and four-stranded (Holliday junction) recombination structures, without sequence specificity. We summarize our experiments showing that purified T4 enzymes catalyze complete unidirectional replication of a plasmid containing the T4 ori(uvsY) origin, with a preformed 9 loop at the position of the 9 loop identified at this origin in vivo. This replication depends on the 41 helicase and is strongly stimulated by 59 protein. Moreover, the helicase-loading protein helps to coordinate leading and lagging strand synthesis by blocking replication on the ori(uvsY) R loop plasmid until the helicase is loaded. The T4 enzymes also can replicate plasmids with 9 loops that do not have a T4 origin sequence, but only if the 9 loops are within an easily unwound DNA sequence.