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Dynamics Of Dna Replication Loops Reveal Temporal Control Of Lagging-strand Synthesis

机译：Dna复制环的动力学揭示了滞后链合成的时间控制

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摘要

In all organisms, the protein machinery responsible for the replication of DNA, the replisome, is faced with a directionality problem. The antiparallel nature of duplex DNA permits the leading-strand polymerase to advance in a continuous fashion, but forces the lagging-strand polymerase to synthesize in the opposite direction. By extending RNA primers, the lagging-strand polymerase restarts at short intervals and produces Okazaki fragments. At least in prokaryotic systems, this directionality problem is solved by the formation of a loop in the lagging strand of the replication fork to reorient the lagging-strand DNA polymerase so that it advances in parallel with the leading-strand polymerase. The replication loop grows and shrinks during each cycle of Okazaki fragment synthesis. Here we use single-molecule techniques to visualize, in real time, the formation and release of replication loops by individual replisomes of bacteriophage T7 supporting coordinated DNA replication. Analysis of the distributions of loop sizes and lag times between loops reveals that initiation of primer synthesis and the completion of an Okazaki fragment each serve as a trigger for loop release. The presence of two triggers may represent a fail-safe mechanism ensuring the timely reset of the replisome after the synthesis of every Okazaki fragment.
机译：在所有生物中，负责DNA复制的蛋白质机制即复制体都面临方向性问题。双链体DNA的反平行性质允许前导链聚合酶以连续方式进行，但会迫使落后链聚合酶沿相反方向合成。通过延伸RNA引物，落后链聚合酶会在短时间内重新启动并产生冈崎片段。至少在原核系统中，该方向性问题通过在复制叉的滞后链中形成环以重新定向滞后链DNA聚合酶以使其与前导链聚合酶平行进行来解决。在Okazaki片段合成的每个周期中，复制循环都会增长和收缩。在这里，我们使用单分子技术实时观察支持协同DNA复制的噬菌体T7的各个复制体对复制环的形成和释放。对环大小的分布和环之间的滞后时间的分析表明，引物合成的开始和冈崎片段的完成均充当环释放的触发。两个触发器的存在可能代表一种故障保护机制，可确保在合成每个Okazaki片段后及时重置复制体。

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