GEMC1 is a TopBP1-interacting protein required for chromosomal DNA replication

Area of Science:

• Molecular Biology
• Cell Biology
• Genetics

Background:

• DNA replication mechanisms are well-studied in unicellular eukaryotes but poorly understood in multicellular organisms.
• Identifying key regulators of DNA replication in vertebrates is crucial for understanding cell proliferation and development.

Purpose of the Study:

• To identify novel factors involved in chromosomal DNA replication in vertebrates.
• To elucidate the role of the newly identified GEMC1 protein in DNA replication initiation.

Main Methods:

• Utilized Xenopus laevis egg extract for biochemical assays.
• Employed protein interaction studies, including binding assays and co-immunoprecipitation.
• Investigated protein phosphorylation using kinase assays.
• Assessed DNA replication initiation by monitoring Cdc45 loading onto chromatin.
• Used morpholino and siRNA to inhibit GEMC1 expression in vertebrate cells.

Main Results:

• Identified GEMC1 (geminin coiled-coil containing protein 1), a conserved vertebrate protein essential for DNA replication.
• Demonstrated that xGEMC1 binds to TopBP1, facilitating its chromatin recruitment during pre-replication complex formation.
• Showed that xGEMC1 interacts with Cdc45 and Cdk2-CyclinE, and its phosphorylation by Cdk2-CyclinE stimulates replication initiation.
• Found that depletion of xGEMC1 impairs Cdc45 loading and prevents DNA replication onset.
• Confirmed that inhibiting GEMC1 expression blocks DNA replication in embryonic and somatic vertebrate cells.

Conclusions:

• GEMC1 is a novel, essential factor for chromosomal DNA replication initiation in multicellular organisms.
• GEMC1 acts by mediating the TopBP1- and Cdk2-dependent recruitment of Cdc45 to replication origins.
• This finding advances our understanding of DNA replication regulation in vertebrates.