直接觀測DNA有助于更好地研究遺傳物質(zhì)的復(fù)制和修復(fù)情況,。
文章第一作者、加州州立大學(xué)（University of California）博士后學(xué)者 Roberto Galletto說：“我們可以直接對復(fù)制和修復(fù)過程進行監(jiān)控,，獲得新的發(fā)現(xiàn)。” 研究詳細結(jié)果刊登在9月20日電子版《Nature》雜志上,。
大腸桿菌（E. coli bacteria）的RecA酶,，能夠延著長鏈DNA延伸,，與DNA形成細絲狀結(jié)構(gòu)（filament）。一條完整的DNA延著RecA排列,，其它DNA可以與母鏈的缺口部分進行交換,，以填補缺口,。在人體中的Rad51蛋白發(fā)揮相似功能,，有研究顯示Rad51與乳腺癌有關(guān),。
論文高級作者、加州大學(xué)分子和細胞生物學(xué)教授,、遺傳和發(fā)育實驗室主任Stephen Kowalczykowski說：“RecA和Rad51組裝filament的過程決定了DNA修復(fù)效果,，但目前對于組裝的機制還知之甚少。”
Galletto將一小片段DNA附著在微小橡膠粒上,，然后將小橡膠粒注入由激光“鑷子”控制的流動小室（chamber）,，橡膠粒上的DNA能夠“隨波逐流”,。Galletto用激光輕輕將這些像水草一樣在液體中漂動的DNA推出小室，推到鄰近的一個含有熒光標記RecA的通道里,。短暫的停留后,，再將DNA推回原先的小室。
對同一DNA重復(fù)上述浸占過程,，結(jié)果每一DNA上附著了4-5個RecA,。一旦這些RecA在DNA上成串排列，DNA/RecA形成的細絲會迅速向兩端延伸,。Kowalczykowski認為實驗過程中使用的這種技術(shù)為將來研究RecA和Rad51提供了很好的參考。
實驗中采用的方法是在Kowalczykowski 和分子細胞生物學(xué)家Ronald J. Baskin早期研究一種解鏈酶工作情況時使用的方法上發(fā)展起來的,。當時的研究結(jié)果刊登于2001年Nature雜志上,。
研究經(jīng)費來源于Jeane B. Kempner頒發(fā)給Galletto的獎金和美國國立衛(wèi)生研究院的資助。
英文原文：
Watching DNA Repair In Real Time
"We can monitor the process directly, and that gives us a different perspective," said Roberto Galletto, a postdoctoral scholar at UC Davis and first author on a paper published Sept. 20 on the Web site of the journal Nature.
In E. coli bacteria, molecules of an enzyme called RecA attach themselves along a DNA strand, stretching it out and forming a filament. A piece of complementary DNA lines up along side it, and pieces of DNA can be swapped in to repair gaps in the original strand. A similar protein, called Rad51, does the same job in humans.
"How RecA and Rad51 assemble into filaments determines the outcome of DNA repair, but very little is known about how assembly is controlled," said senior author Stephen Kowalczykowski, professor in the sections of Microbiology and of Molecular and Cellular Biology and director of the Center for Genetics and Development at UC Davis. Genes that control the human gene, Rad51, have been linked to increased risk of breast cancer.
Galletto attached a short piece of DNA to a tiny latex bead and placed it in a flow chamber, held by laser beam "tweezers." Fluid flowing past made the DNA stream out like a banner. Then he nudged it into an adjacent channel containing fluorescently-tagged RecA. After short intervals of time, he moved it back to the first chamber to observe the results.
By repeatedly dipping the same piece of DNA into the fluorescent channel, the researchers could see the RecA form clusters of four to five molecules on the DNA. Once those clusters had formed, the DNA/RecA filament rapidly grew in both directions. The measurements made in those experiments will be the baseline for future studies of both RecA and Rad51, Kowalczykowski said.
The new work adapts an approach developed by Kowalczykowski and Ronald J. Baskin, professor of molecular and cellular biology, to study single enzymes at work unwinding DNA strands. That research was first published in Nature in 2001.
In addition to Galletto, Kowalczykowski and Baskin, the research team included postdoctoral scholar Ichiro Amitani. The work was funded by the National Institutes of Health and a fellowship awarded to Galletto by the Jeane B. Kempner Foundation
