專題：Nature報導
DNA複製是活體生物的基本生命過程，允許細胞進行分裂和增殖，並維持原始細胞的遺傳編碼和適當功能。對於該過程或機制的理解，也出現了很多挑戰，比如雙螺旋的DNA分離成兩個股鏈後，這兩股鏈會用不同的方式進行複製，然而卻能同時完成複製。
根據12月17日Nature上的一篇文章，在一項由美國羅伯特伍德詹森醫學院和伊利諾斯大學共同完成的研究中，科學家關注了上述重要的問題。研究識別了3種重要的方式，解答了科學家關於DNA雙鏈同時完成拷貝的疑問。
DNA複製是一個重要的過程，對於活細胞的生存和增殖來說是必須的。這同樣也是一個已經被研究了十幾年的複雜問題，但是對於兩條鏈同時完成拷貝的機制還不是很清楚。Smita Patel教授介紹說，這項研究解釋了複製過程是如何協調完成的，DNA複製錯誤能夠導致機體缺陷和疾病，比如癌症。
解旋酶啟動DNA複製，然後通過DNA聚合酶雙鏈會重新生成。一條鏈叫前導鏈會連續不斷的再生，另一條鏈是隨從鏈，通過片段連接重新產生。
研究人員使用state-of-the-art方法在毫秒水平測量DNA合成的過程。研究表明，短片段是以很快的速率合成的，因此隨從鏈的合成能夠和前導鏈的合成保持一致。
研究人員捕獲了DNA生成過程中的複製酶，識別了3種DNA雙鏈同時完成複製的方式。研究人員注意到，隨從鏈的聚合酶會以更快的速度跟隨著前導鏈的聚合酶，這就給隨從鏈聚合酶額外的時間重新開始新片段的生成。這項發現也支持了先前由加利福尼亞大學生化教授Bruce Alberts提出的模型。
此外，研究人員表示，根據RNA引物的產生過程，複製的時間將進一步縮減。因此，隨從鏈合成酶的快速移動，使得RNA引物產生提前，聚合酶能夠快速捕獲RNA引物，使得雙鏈能夠同時完成複製。（生物谷Bioon.com）
生物谷推薦原始出處：
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.