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Updated: Aug 12, 2026

Visualization of DNA Replication in the Vertebrate Model System DT40 using the DNA Fiber Technique
Published on: October 27, 2011
Cdc7-Drf1 is a developmentally regulated protein kinase required for the initiation of vertebrate DNA replication
Tatsuro S Takahashi1, Johannes C Walter
1Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA.
Abstract:
Cdc7, a protein kinase required for the initiation of eukaryotic DNA replication, is activated by a regulatory subunit, Dbf4. A second activator of Cdc7 called Drf1 exists in vertebrates, but its function is unknown. Here, we report that in Xenopus egg extracts, Cdc7-Drf1 is far more abundant than Cdc7-Dbf4, and removal of Drf1 but not Dbf4 severely inhibits phosphorylation of Mcm4 and DNA replication. After gastrulation, when the cell cycle acquires somatic characteristics, Drf1 levels decline sharply and Cdc7-Dbf4 becomes the more abundant kinase. These results identify Drf1 as a developmentally regulated, essential activator of Cdc7 in Xenopus.
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