Gao Hui, Chen Xiao-Bo, McGowan Clare H
Department of Molecular Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
Mol Biol Cell. 2003 Dec;14(12):4826-34. doi: 10.1091/mbc.e03-05-0276.
Mus81 is a highly conserved substrate specific endonuclease. Human Mus81 cleaves Holliday junctions, replication forks, and 3' flap substrates in vitro, suggesting a number of possible in vivo functions. We show here that the abundance of human Mus81 peaks in S-phase and remains high in cells that have completed DNA replication and that Mus81 is a predominantly nuclear protein, with super accumulation in nucleoli. Two RecQ related DNA helicases BLM and WRN that are required for recombination repair in human cells colocalize with Mus81 in nucleoli. However, the nucleolar retention of Mus81 is not dependent on the presence of BLM or WRN, or on ongoing transcription. Mus81 is recruited to localized regions of UV damage in S-phase cells, but not in cells that are blocked from replicating DNA or that have completed replication. The retention of human Mus81 at regions of UV-induced damage specifically in S-phase cells suggest that the enzyme is recruited to the sites at which replication forks encounter damaged DNA. The nucleolar concentration of Mus81 suggests that it is required to repair problems that arise most frequently in the highly repetitive nucleolar DNA. Together these data support a role for Mus81 in recombination repair in higher eukaryotes.
Mus81是一种高度保守的底物特异性核酸内切酶。人源Mus81在体外可切割霍利迪连接体、复制叉和3' 翼状底物，这表明其在体内可能具有多种功能。我们在此表明，人源Mus81的丰度在S期达到峰值，并且在完成DNA复制的细胞中仍保持较高水平，而且Mus81主要是一种核蛋白，在核仁中大量积累。在人类细胞中参与重组修复所需的两种RecQ相关DNA解旋酶BLM和WRN与Mus81在核仁中共定位。然而，Mus81在核仁中的保留并不依赖于BLM或WRN的存在，也不依赖于正在进行的转录。Mus81在S期细胞中被招募到紫外线损伤的局部区域，但在DNA复制受阻或已完成复制的细胞中则不会。人源Mus81特异性地在S期细胞的紫外线诱导损伤区域保留，这表明该酶被招募到复制叉遇到受损DNA的位点。Mus81在核仁中的集中表明它对于修复高度重复的核仁DNA中最常出现的问题是必需的。这些数据共同支持了Mus81在高等真核生物重组修复中的作用。
