（封面圖片：細(xì)菌DNA轉(zhuǎn)位蛋白FtsK的三個(gè)γ域,，它們與一個(gè)8堿基對(duì)KOPS序列結(jié)合,。）
環(huán)狀染色體二聚體是由于姊妹染色單體之間的重組而產(chǎn)生的，它們在細(xì)胞分裂的過程中無法被成功分離到子代細(xì)胞當(dāng)中,。在2008年8月22日出版的《分子細(xì)胞》（Molecular Cell）上,，來自英國的一組科學(xué)家發(fā)表了他們的最新研究結(jié)果，他們表示通過研究找到了一種細(xì)菌DNA轉(zhuǎn)位蛋白-FtsK的3個(gè)γ區(qū)域,，并且闡述了這種轉(zhuǎn)位蛋白對(duì)于DNA負(fù)載和染色體重組等發(fā)生作用的內(nèi)部機(jī)制,。
研究人員對(duì)大腸埃希氏菌（Escherichia coli）研究后發(fā)現(xiàn)，在該細(xì)菌的dif位點(diǎn)的XerCD位點(diǎn)特異性重組能將這些二聚體染色體轉(zhuǎn)化為染色單體,，這一過程中伴隨著一個(gè)需要DNA轉(zhuǎn)位酶（DNA translocase）FtsK的反應(yīng),。其中染色體上的一段小型8堿基對(duì)DNA序列KOPS（GGGNAGGG）引導(dǎo)著FtsK的轉(zhuǎn)位發(fā)生。而FtsK通過一個(gè)C端翼狀螺旋γ域來和KOPS序列發(fā)生相互作用,。
對(duì)于3個(gè)與KOPS序列結(jié)合的FtsKγ域的晶體結(jié)構(gòu)分析,，幫助科學(xué)家了解了這些γ域是如何識(shí)別KOPS序列的。因此,，研究小組推測每個(gè)FtsK六聚體中存在3個(gè)γ域?qū)τ谧R(shí)別KOPS序列并且負(fù)載上FtsK是夠用的,，這將最終激活dif位點(diǎn)的重組發(fā)生。而在轉(zhuǎn)位過程中,，F(xiàn)tsK無法識(shí)別顛倒的KOPS序列,。因此,，文章作者提出，KOPS序列是作為FtsK負(fù)載位點(diǎn)存在的,，以上這種特殊的γ-KOPS之間的結(jié)合方式控制著FtsK馬達(dá)區(qū)域,，并且最終決定著其運(yùn)動(dòng)的單一方向。（生物谷Bioon.com）
生物谷推薦原始出處：
Molecular Cell,，Vol 31, 498-509, 22 August 2008,，Jan L?we, Ian Grainge
Molecular Mechanism of Sequence-Directed DNA Loading and Translocation by FtsK
Jan Löwe,1, Antti Ellonen,2 Mark D. Allen,3 Claire Atkinson,2 David J. Sherratt,2 and Ian Grainge2,
1 MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 0QH, UK
2 Department of Biochemistry, University of Oxford, Oxford OX1 3QU, UK
3 Centre for Protein Engineering, MRC, Hills Road, Cambridge CB2 0QH, UK
Corresponding author
Dimeric circular chromosomes, formed by recombination between monomer sisters, cannot be segregated to daughter cells at cell division. XerCD site-specific recombination at the Escherichia coli dif site converts these dimers to monomers in a reaction that requires the DNA translocase FtsK. Short DNA sequences, KOPS (GGGNAGGG), which are polarized toward dif in the chromosome, direct FtsK translocation. FtsK interacts with KOPS through a C-terminal winged helix domain γ. The crystal structure of three FtsKγ domains bound to 8 bp KOPS DNA demonstrates how three γ domains recognize KOPS. Using covalently linked dimers of FtsK, we infer that three γ domains per hexamer are sufficient to recognize KOPS and load FtsK and subsequently activate recombination at dif. During translocation, FtsK fails to recognize an inverted KOPS sequence. Therefore, we propose that KOPS act solely as a loading site for FtsK, resulting in a unidirectionally oriented hexameric motor upon DNA.
