双链断裂的DNA能够以其同源染色体为模板，通过同源重组的方式修复，这一过程对DNA复制、DNA损伤的修复及减数分裂中重组和同源染色体分离等有重要作用。
在减数分裂过程中，由Spo11蛋白质催化形成断裂双链，RecA族蛋白结合于断裂的DNA末端形成DNA－蛋白 质细丝，能够催化同源配对，使单链DNA末端入侵其同源区段，Rad51和Dmc1两个RecA的同源蛋白在此过程中起重要作用。但是科学家对入侵后的同源重组过程则了解得比较少。
来自美国加利福尼亚大学和日本大阪大学的研究人员以芽殖酵母为研究对象，采用双向电泳和Southern杂交等主要技术，对同源重组的入侵后过程进行研究，结果发现无论交换和非交换的同源重组，Rad52在入侵后过程中均起重要作用，能够催化DNA互补序列退火，该活性存在于Rad52的N末端结构域。
在前期DNA末端入侵同源染色体时，Rad51的结合也必需由Rad52催化，而在入侵后阶段Rad52自身能够催化DNA互补序列退火，并且和Rad51的富集无关。可见Rad52在通过同源重组修复断裂双链的不同阶段均有着非常重要的作用，与同源互补序列的退火密切相关。异常交换可能导致染色体重排、同源染色体的错误分离等致命突变，而适当调节Rad52的活性可能抑制异常交换的发生。
该研究结果发表于2008年2月29日的《分子细胞》（Molecular Cell）杂志上。（科学网 穆宏平/编译）
生物谷推荐原始出处：
（Molecular Cell），Vol 29, 517-524, 29 February 2008，Jessica P. Lao, Neil Hunter
Rad52 Promotes Postinvasion Steps of Meiotic Double-Strand-Break Repair
Jessica P. Lao,1,2 Steve D. Oh,1,2 Miki Shinohara,3 Akira Shinohara,3 and Neil Hunter1,2,
1 Section of Microbiology, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA
2 Section of Molecular and Cellular Biology, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA
3 Institute for Protein Research, Graduate School of Science, Osaka University, Suita 565-0871, Japan
Corresponding author
Neil Hunter
nhunter@ucdavis.edu
Summary
During DNA double-strand-break (DSB) repair by recombination, the broken chromosome uses a homologous chromosome as a repair template. Early steps of recombination are well characterized: DSB ends assemble filaments of RecA-family proteins that catalyze homologous pairing and strand-invasion reactions. By contrast, the postinvasion steps of recombination are poorly characterized. Rad52 plays an essential role during early steps of recombination by mediating assembly of a RecA homolog, Rad51, into nucleoprotein filaments. The meiosis-specific RecA-homolog Dmc1 does not show this dependence, however. By exploiting the Rad52 independence of Dmc1, we reveal that Rad52 promotes postinvasion steps of both crossover and noncrossover pathways of meiotic recombination in Saccharomyces cerevisiae. This activity resides in the N-terminal region of Rad52, which can anneal complementary DNA strands, and is independent of its Rad51-assembly function. Our findings show that Rad52 functions in temporally and biochemically distinct reactions and suggest a general annealing mechanism for reuniting DSB ends during recombination.
