Cdc48p is a highly conserved protein found in eukaryotes. It belongs to the AAA⁺ super family which is involved in many cellular functions, including protein degradation, cell cycle progression, membrane fusion and apoptosis. A novel function of Cdc48p in DNA replication has been proposed in recent years. It has been shown that CDC-48^UFD-1/NPL-4 complex is required for efficient DNA replication in C. elegans. CDT-1 degradation coordinated by CDC-48/p97 allows chromatin dissociation of GINS to ensure faithful DNA replication. In budding yeast, we also identified an essential role of Cdc48p in DNA replication. We found that Cdc48p binds to chromatin and interacts with some of the pre-RC (pre-replicative complex) components, Orc1p, Orc3p and Mcm2p. The temperature sensitive mutan...[ Read more ]

Cdc48p is a highly conserved protein found in eukaryotes. It belongs to the AAA⁺ super family which is involved in many cellular functions, including protein degradation, cell cycle progression, membrane fusion and apoptosis. A novel function of Cdc48p in DNA replication has been proposed in recent years. It has been shown that CDC-48^UFD-1/NPL-4 complex is required for efficient DNA replication in C. elegans. CDT-1 degradation coordinated by CDC-48/p97 allows chromatin dissociation of GINS to ensure faithful DNA replication. In budding yeast, we also identified an essential role of Cdc48p in DNA replication. We found that Cdc48p binds to chromatin and interacts with some of the pre-RC (pre-replicative complex) components, Orc1p, Orc3p and Mcm2p. The temperature sensitive mutant, cdc48-3, has a high plasmid loss rate, consistent with the 2D gel analysis showing that DNA replication is defective in the mutant at the restrictive temperature. Impaired loading of Mcm2-7 complex in DNA re-replication system further supports this hypothesis. Moreover, defects in dephosphorylation of Orc6p were also detected in the mutant, consistent with pre-RC formation impairment. Orc6p is a substrate of Cdc14p which is a phosphatase involved in resetting the competency of replication licensing by dephosphorylating multiple initiation proteins. We showed that Cdc48p inactivation caused functional defects in Cdc14p, which in turn led to failure of dephosphorylation of Orc6p. In support, Cdc48p co-precipitated with Cdc14p. Ufd1p and Npl4p are cofactors of Cdc48p. They form the Cdc48p^Ufd1p/Npl4p complex, which is responsible for protein degradation. Inactivation of the two proteins causes defects in DNA replication in the DNA re-replication system. I propose that the Cdc48p^Ufd1p/Npl4p complex associates with Cdc14p to form an active complex or the Cdc48p^Ufd1p/Npl4p complex degrades the inhibitor of a cofactor of Cdc14p to activate Cdc14p. Further studies of the interaction between Cdc48p and Cdc14p will elucidate the mechanism of Cdc48p in the regulation of DNA replication.