Bleuit J S, Xu H, Ma Y, Wang T, Liu J, Morrical S W
Department of Biochemistry, University of Vermont College of Medicine, Burlington, VT 05405, USA.
Proc Natl Acad Sci U S A. 2001 Jul 17;98(15):8298-305. doi: 10.1073/pnas.131007498.
Studies of recombination-dependent replication (RDR) in the T4 system have revealed the critical roles played by mediator proteins in the timely and productive loading of specific enzymes onto single-stranded DNA (ssDNA) during phage RDR processes. The T4 recombination mediator protein, uvsY, is necessary for the proper assembly of the T4 presynaptic filament (uvsX recombinase cooperatively bound to ssDNA), leading to the recombination-primed initiation of leading strand DNA synthesis. In the lagging strand synthesis component of RDR, replication mediator protein gp59 is required for the assembly of gp41, the DNA helicase component of the T4 primosome, onto lagging strand ssDNA. Together, uvsY and gp59 mediate the productive coupling of homologous recombination events to the initiation of T4 RDR. UvsY promotes presynaptic filament formation on 3' ssDNA-tailed chromosomes, the physiological primers for T4 RDR, and recent results suggest that uvsY also may serve as a coupling factor between presynapsis and the nucleolytic resection of double-stranded DNA ends. Other results indicate that uvsY stabilizes uvsX bound to the invading strand, effectively preventing primosome assembly there. Instead, gp59 directs primosome assembly to the displaced strand of the D loop/replication fork. This partitioning mechanism enforced by the T4 recombination/replication mediator proteins guards against antirecombination activity of the helicase component and ensures that recombination intermediates formed by uvsX/uvsY will efficiently be converted into semiconservative DNA replication forks. Although the major mode of T4 RDR is semiconservative, we present biochemical evidence that a conservative "bubble migration" mode of RDR could play a role in lesion bypass by the T4 replication machinery.
对T4系统中依赖重组的复制（RDR）的研究揭示了介导蛋白在噬菌体RDR过程中，将特定酶及时且高效地加载到单链DNA（ssDNA）上所发挥的关键作用。T4重组介导蛋白uvsY是T4突触前细丝（uvsX重组酶与ssDNA协同结合）正确组装所必需的，从而导致前导链DNA合成的重组引发起始。在RDR的滞后链合成组件中，复制介导蛋白gp59是将T4引发体的DNA解旋酶组件gp41组装到滞后链ssDNA上所必需的。uvsY和gp59共同介导同源重组事件与T4 RDR起始的有效偶联。UvsY促进在3' ssDNA尾染色体上形成突触前细丝，这是T4 RDR的生理引物，最近的结果表明uvsY也可能作为突触前和双链DNA末端核酸酶切除之间的偶联因子。其他结果表明uvsY稳定与侵入链结合的uvsX，有效地防止在那里组装引发体。相反，gp59将引发体组装引导至D环/复制叉的置换链。由T4重组/复制介导蛋白执行的这种分配机制可防止解旋酶组件的抗重组活性，并确保由uvsX/uvsY形成的重组中间体将有效地转化为半保留DNA复制叉。虽然T4 RDR的主要模式是半保留的，但我们提供了生化证据表明保守的“气泡迁移”RDR模式可能在T4复制机制绕过损伤中发挥作用。
