Distinct Cdc7 functions in the context of DNA replication and mitosis

细胞分裂过程受到严格调控，并与其遗传物质（DNA）的复制密切协调。在哺乳动物细胞中，在单个细胞分裂周期中，基因组必须仅完整复制一次。这一过程的紊乱对细胞来说可能是致命的，或者导致遗传不稳定。每细胞周期一次的复制主要是通过严格调控复制前复合物（pre-RC）的逐步形成和激活来实现的。在这种调节的最后阶段，Cdc 7蛋白作为“分子开关”，通过磷酸化前RC的关键许可组分来激活DNA复制。众所周知，Cdc 7本身受Dbf 4蛋白的调节。然而，Cdc 7和Dbf 4调节亚基如何相互结合以在复制起始位点激活pre-RC的机制尚不清楚。我们最近的数据表明，Cdk 1介导的Cdc 7磷酸化导致Cdc 7与CRM 1蛋白的亲和力增加。因此，磷酸化Cdc 7从复制起始位点解离并被CRM 1结合，从而Cdc 7被隔离在细胞质中。因此，Cdc 7磷酸化阻止了G2-M期间的DNA再复制，这对于维持遗传稳定性至关重要。随着细胞在下一轮细胞分裂周期中从G1期进展到S期，Cdc 7作为复制激活剂的功能通过被称为磷酸酶的酶去除其磷酸基团而“恢复”。实际上，负责Cdc 7去磷酸化的酶作为Cdc 7-Dbf 4激活DNA复制的关键分子开关发挥作用。我们的主要目标是确定和表征这种重要的去磷酸化酶。此外，我们还计划确定磷酸化Cdc 7是否具有其他功能。这项工作的数据将为细胞周期进程中DNA复制的调控提供令人兴奋的新线索。我们的数据还将为细胞如何保持其遗传稳定性的控制机制提供巨大的洞察力。如果成功，这项工作将对DNA复制和细胞周期研究领域产生非常重大和持久的影响。

The cell division process is tightly regulated and closely coordinated with copying of its genetic material (DNA). In mammalian cells, the genome must replicate only once in its entirety during a single cell division cycle. Derangement of this process can be fatal for the cell or result in genetic instability. The once-per-cell cycle replication is achieved mainly by strictly regulating the stepwise formation and activation of pre-replication complex (pre-RC). At final stage of this regulation, Cdc7 protein functions as a 'molecular switch' for the activation of DNA replication by phosphorylating critical licensing components of the pre-RC. It is well known that Cdc7 itself is regulated by Dbf4 protein. However, it is not well-understood the mechanism how Cdc7 and the Dbf4 regulatory subunit bind each other to activate the pre-RC at the replication start-site. Our recent data shows that the Cdk1-mediated Cdc7 phosphorylation causes an increase in Cdc7 affinity to CRM1 protein. As a result, phosphorylated Cdc7 is dissociated from replication start-sites and bound by CRM1, by which Cdc7 is sequestered in the cytoplasm. Thus, Cdc7 phosphorylation prevents DNA re-replication during G2-M, which is critical for maintaining genetic stability. As a cell progresses from G1 to S phase during the next round of cell division cycle, the function of Cdc7 as replication activator is 'restored' by removing its phosphate group by an enzyme called phosphatase. In effect, the enzyme responsible for Cdc7 dephosphorylation functions as a key molecular switch toward the activation of DNA replication by Cdc7-Dbf4. Our main objective is to identify and characterize this important dephosphorylation enzyme. In addition, we also plan to determine whether phosphorylated Cdc7 has other functions. Data from this proposed work will shed exciting new light on the regulation of DNA replication in the context of cell cycle progression. Our data will also provide tremendous insight into the control mechanism about how a cell maintains its genetic stability. If successful, this work can have very significant and lasting impact on the DNA replication and cell cycle research fields.