Lau Eric, Zhu Changjun, Abraham Robert T, Jiang Wei
The Burnham Institute, La Jolla, California 92037, USA.
EMBO Rep. 2006 Apr;7(4):425-30. doi: 10.1038/sj.embor.7400624. Epub 2006 Jan 27.
The Cdc6 protein is required for licensing of replication origins before the onset of DNA replication in eukaryotic cells. Here, we examined whether Cdc6 has other roles in mammalian cell-cycle progression from S to G2/M phase. Using RNA interference, we showed that depletion of Cdc6 in synchronous G1 cells blocks G1 to S transition, confirming the essential role of Cdc6 in the initiation of DNA replication. In contrast, depletion of Cdc6 in synchronous S-phase cells slowed DNA replication and led to mitotic lethality. The Cdc6-depleted S-phase cells showed fewer newly fired origins; however, established replication forks remained active, even during chromatin condensation. Despite such DNA replication abnormalities, loss of Cdc6 failed to activate Chk1 kinase. These results show that Cdc6 is not only required for G1 origin licensing, but is also crucial for proper S-phase DNA replication that is essential for DNA segregation during mitosis.
Cdc6蛋白是真核细胞DNA复制开始前复制起点许可所必需的。在此，我们研究了Cdc6在哺乳动物细胞从S期到G2/M期的细胞周期进程中是否具有其他作用。使用RNA干扰技术，我们发现同步化G1期细胞中Cdc6的缺失会阻断G1期到S期的转变，证实了Cdc6在DNA复制起始中的重要作用。相反，同步化S期细胞中Cdc6的缺失会减缓DNA复制并导致有丝分裂致死。Cdc6缺失的S期细胞中新启动的复制起点较少；然而，已建立的复制叉仍保持活跃，即使在染色质浓缩期间也是如此。尽管存在这种DNA复制异常，但Cdc6的缺失未能激活Chk1激酶。这些结果表明，Cdc6不仅是G1期复制起点许可所必需的，而且对于有丝分裂期间DNA分离所必需的正确S期DNA复制也至关重要。
