Kanemaki Masato, Labib Karim
Cancer Research UK.
EMBO J. 2006 Apr 19;25(8):1753-63. doi: 10.1038/sj.emboj.7601063. Epub 2006 Apr 6.
The Cdc45 protein is crucial for the initiation of chromosome replication in eukaryotic cells, as it allows the activation of prereplication complexes (pre-RCs) that contain the MCM helicase. This causes the unwinding of origins and the establishment of DNA replication forks. The incorporation of Cdc45 at nascent forks is a highly regulated and poorly understood process that requires, in budding yeast, the Sld3 protein and the GINS complex. Previous studies suggested that Sld3 is also important for the progression of DNA replication forks after the initiation step, as are Cdc45 and GINS. In contrast, we show here that Sld3 does not move with DNA replication forks and only associates with MCM in an unstable manner before initiation. After the establishment of DNA replication forks from early origins, Sld3 is no longer essential for the completion of chromosome replication. Unlike Sld3, GINS is not required for the initial recruitment of Cdc45 to origins and instead is necessary for stable engagement of Cdc45 with the nascent replisome. Like Cdc45, GINS then associates stably with MCM during S-phase.
Cdc45蛋白对于真核细胞中染色体复制的起始至关重要，因为它能激活包含MCM解旋酶的复制前复合体（pre-RC）。这会导致复制起点解旋并建立DNA复制叉。Cdc45在新生复制叉上的掺入是一个高度受调控且了解甚少的过程，在芽殖酵母中，这需要Sld3蛋白和GINS复合体。先前的研究表明，Sld3对于DNA复制起始步骤之后复制叉的推进也很重要，Cdc45和GINS也是如此。相比之下，我们在此表明，Sld3不会随着DNA复制叉移动，并且在起始之前仅以不稳定的方式与MCM结合。从早期复制起点建立DNA复制叉之后，Sld3对于染色体复制的完成不再是必需的。与Sld3不同，GINS对于Cdc45最初募集到复制起点不是必需的，而是Cdc45与新生复制体稳定结合所必需的。与Cdc45一样，GINS随后在S期与MCM稳定结合。
