生物谷报道:美国圣犹大儿童研究医院(St. Jude Children's Research Hospital)的科学家,利用染色质免疫沉淀技术(Chromatin Immunoprecipitation,简称ChIP)以及修饰过的I-Ppol酵素(一种能切断DNA的酵素)来研究DNA双股断裂(DNA double-strand breaks,简称DSBs)时蛋白质参与修复的机制,除了鉴定出参与DNA修复的蛋白质外,也观察到这些蛋白质作用的先后顺序,此研究发表于5月7日的Nature Cell Biology期刊。
Kastan医师说:「若缺乏ATM及NBS1这两个修复蛋白,DSBs的修复就无法正常运作,若ATM的功能失常就会产生毛细管扩张失调症(ataxia-teleangiectasia),导致神经退化并有严重的癌症发生率,若NBS1的功能失常则会导致Nijmegen breakage syndrome,同样也会有发生癌症或损坏DNA无法修复的情况。」
主导实验进行的Elijahu Berkovich博士表示:“这些修复DNA的蛋白质包括ATM, NBS1, XRCC4以及gamma-H2AX。首先NBS1蛋白会招募ATM蛋白到DNA的断裂处,然后一起将被蛋白质缠绕住的DNA解开,使断裂处的DNA能裸露,让其它参与修复DNA的蛋白质能陆续开始工作,另外,只有在ATM及NSB1蛋白的存在下,才能确保修复因子(repair factor)XRCC4能到达DNA断裂处进行修补的程序。研究人员还发现一开始与DNA断裂处结合的是ATM蛋白,直到XRCC4蛋白抵达时,ATM蛋白才会被取代。”
这项研究具有十分重要的意义,因为若无法精确的完成这些修复程序,可能会导致基因突变、细胞死亡或是癌症的产生,此外,经由这些DNA修复机制的了解,也能阻断癌细胞中DSBs的修复,使癌细胞走向死亡的境地。Michael Kastan医师表示:“在此研究之前,并无有效的方法可研究DNA修复蛋白群(DNA repair proteins)的工作情况,而此研究则克服了许多困难,将双股DNA断裂后,许多蛋白质参与修复DNA的情况详细地呈现。”
(资料来源 : Bio.com)
英文原文链接:
原始出处:
Nature Cell Biology
Published online: 7 May 2007; | doi:10.1038/ncb1599
Roles of ATM and NBS1 in chromatin structure modulation and DNA double-strand break repair
Elijahu Berkovich1, Raymond J. Monnat Jr.2 & Michael B. Kastan1
1 Department of Oncology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA.
2 Departments of Pathology and of Genome Sciences, University of Washington, Box 357705, Seattle, WA 98195–7705, USA.
Correspondence should be addressed to Michael B. Kastan michael.kastan@stjude.org
Abstract
We developed a novel system to create DNA double-strand breaks (DSBs) at defined endogenous sites in the human genome, and used this system to detect protein recruitment and loss at and around these breaks by chromatin immunoprecipitation (ChIP). The detection of human ATM protein at site-specific DSBs required functional NBS1 protein, ATM kinase activity and ATM autophosphorylation on Ser 1981. DSB formation led to the localized disruption of nucleosomes, a process that depended on both functional NBS1 and ATM. These two proteins were also required for efficient recruitment of the repair cofactor XRCC4 to DSBs, and for efficient DSB repair. These results demonstrate the functional importance of ATM kinase activity and phosphorylation in the response to DSBs, and support a model in which ordered chromatin structure changes that occur after DNA breakage depend on functional NBS1 and ATM, and facilitate DNA DSB repair.