DNA复制是活体生物的基本生命过程，允许细胞进行分裂和增殖，并维持原始细胞的遗传编码和适当功能。对于该过程或机制的理解，也出现了很多挑战，比如双螺旋的DNA分离成两个股链后，这两股链会用不同的方式进行复制，然而却能同时完成复制。
根据12月17日Nature上的一篇文章，在一项由美国罗伯特伍德约翰逊医学院和伊利诺斯大学共同完成的研究中，科学家关注了上述重要的问题。研究识别了3种重要的方式，解答了科学家关于DNA双链同时完成拷贝的疑问。
DNA复制是一个重要的过程，对于活细胞的生存和增殖来说是必须的。这同样也是一个已经被研究了十几年的复杂问题，但是对于两条链同时完成拷贝的机制还不是很清楚。Smita Patel教授介绍说，这项研究解释了复制过程是如何协调完成的，DNA复制错误能够导致机体缺陷和疾病，比如癌症。
解旋酶启动DNA复制，然后通过DNA聚合酶双链会重新生成。一条链叫前导链会连续不断的再生，另一条链是随从链，通过片段连接重新产生。
研究人员使用state-of-the-art方法在毫秒水平测量DNA合成的过程。研究表明，短片段是以很快的速率合成的，因此随从链的合成能够和前导链的合成保持一致。
研究人员捕获了DNA生成过程中的复制酶，识别了3种DNA双链同时完成复制的方式。研究人员注意到，随从链的聚合酶会以更快的速度跟随着前导链的聚合酶，这就给随从链聚合酶额外的时间重新开始新片段的生成。这项发现也支持了先前由加利福尼亚大学生化教授Bruce Alberts提出的模型。
此外，研究人员表示，根据RNA引物的产生过程，复制的时间将进一步缩减。因此，随从链合成酶的快速移动，使得RNA引物产生提前，聚合酶能够快速捕获RNA引物，使得双链能够同时完成复制。（生物谷Bioon.com）
生物谷推荐原始出处：
Nature 462, 940-943 (17 December 2009) | doi:10.1038/nature08611
Coordinating DNA replication by means of priming loop and differential synthesis rate
Manjula Pandey1, Salman Syed2, Ilker Donmez1, Gayatri Patel1, Taekjip Ha2,3 & Smita S. Patel1
1 Department of Biochemistry, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, Piscataway, New Jersey 08854, USA
2 Howard Hughes Medical Institute, Urbana, Illinois 61801, USA
3 Department of Physics and the Center for the Physics of Living Cells, University of Illinois, Urbana-Champaign, Illinois 61801, USA
Genomic DNA is replicated by two DNA polymerase molecules, one of which works in close association with the helicase to copy the leading-strand template in a continuous manner while the second copies the already unwound lagging-strand template in a discontinuous manner through the synthesis of Okazaki fragments1, 2. Considering that the lagging-strand polymerase has to recycle after the completion of every Okazaki fragment through the slow steps of primer synthesis and hand-off to the polymerase3, 4, 5, it is not understood how the two strands are synthesized with the same net rate6, 7, 8, 9. Here we show, using the T7 replication proteins10, 11, that RNA primers are made ‘on the fly’ during ongoing DNA synthesis and that the leading-strand T7 replisome does not pause during primer synthesis, contrary to previous reports12, 13. Instead, the leading-strand polymerase remains limited by the speed of the helicase14; it therefore synthesizes DNA more slowly than the lagging-strand polymerase. We show that the primase–helicase T7?gp4 maintains contact with the priming sequence during ongoing DNA synthesis; the nascent lagging-strand template therefore organizes into a priming loop that keeps the primer in physical proximity to the replication complex. Our findings provide three synergistic mechanisms of coordination: first, primers are made concomitantly with DNA synthesis; second, the priming loop ensures efficient primer use and hand-off to the polymerase; and third, the lagging-strand polymerase copies DNA faster, which allows it to keep up with leading-strand DNA synthesis overall.
