Department of Biological Sciences, and Institute for Molecular Biology and Genetics, Seoul National University, Seoul 151-742, Republic of Korea.
Exp Cell Res. 2011 Apr 15;317(7):994-1004. doi: 10.1016/j.yexcr.2011.01.022. Epub 2011 Feb 1.
TopBP1 contains repeats of the BRCA1 C-terminal (BRCT) domain and plays important roles in DNA damage response, DNA replication, and other cellular regulatory functions during the interphase. In prometaphase, metaphase, and anaphase, TopBP1 localizes to the mitotic centrosomes, which function as spindle-poles for the bipolar separation of sister chromatids. The localization of TopBP1 to the mitotic centrosomes is mediated by amino acid residues 1259 to 1420 in the TopBP1 C-terminal region (TbpCtr). GST and DsRed2 tags fused to TbpCtr were localized in the mitotic centrosomes, thereby suggesting that TbpCtr functions as a mitosis-specific centrosome localization signal (CLS). Mutations of Ser 1273 and/or Lys 1317, which were predicted to interact with a putative phosphoprotein, inhibited CLS function. Ectopic expression of TbpCtr specifically eliminated endogenous TopBP1 from the mitotic centrosomes, whereas mutant TbpCtr derivatives, containing substitutions at Ser 1273 and/or Lys 1317, did not. The specific elimination of TopBP1 from the mitotic centrosomes prolonged the durations of prometaphase and metaphase and shortened the inter-kinetochore distances of metaphase sister chromatids while maintaining the spindle assembly checkpoint. These results suggest that the localization of TopBP1 to the mitotic centrosomes is necessary for proper mitotic progression.
TopBP1 含有 BRCA1 C 末端（BRCT）结构域的重复序列，在间期的 DNA 损伤反应、DNA 复制和其他细胞调节功能中发挥重要作用。在前期、中期和后期，TopBP1 定位于有丝分裂中心体，作为姐妹染色单体的两极分离的纺锤体极。TopBP1 定位于有丝分裂中心体是由 TopBP1 C 末端区域（TbpCtr）的 1259 到 1420 个氨基酸残基介导的。GST 和 DsRed2 标签融合到 TbpCtr 中，定位于有丝分裂中心体，这表明 TbpCtr 作为一个有丝分裂特异性中心体定位信号（CLS）起作用。预测与假定磷酸化蛋白相互作用的 Ser1273 和/或 Lys1317 突变，抑制了 CLS 功能。TbpCtr 的异位表达特异性地将内源性 TopBP1 从有丝分裂中心体中去除，而含有 Ser1273 和/或 Lys1317 取代的突变型 TbpCtr 衍生物则不能。TopBP1 从有丝分裂中心体的特异性去除延长了前期和中期的持续时间，并缩短了中期姐妹染色单体的着丝粒间距离，同时保持纺锤体组装检查点。这些结果表明，TopBP1 定位于有丝分裂中心体对于有丝分裂的正常进行是必要的。
