Regulated eukaryotic DNA replication origin firing with purified proteins

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Eukaryotic DNA replication initiates from multiple origins, requiring precise regulation for genome duplication.
• Replication initiation occurs in two steps: minichromosome maintenance (MCM) complex loading in G1, followed by activation to the CMG helicase in S phase.

Purpose of the Study:

• To reconstitute and analyze the minimal protein requirements for regulated DNA replication initiation in vitro.
• To elucidate the roles of cyclin-dependent kinase (CDK) and Dbf4-dependent kinase (DDK) in controlling replication initiation.

Main Methods:

• Reconstitution of budding yeast DNA replication initiation using 16 purified replication factors (42 polypeptides).
• In vitro assays to observe origin-dependent initiation and regulatory mechanisms.

Main Results:

• The reconstituted system recapitulated in vivo regulation of DNA replication initiation.
• CDK inhibits MCM loading by phosphorylating ORC and promotes CMG formation by phosphorylating Sld2 and Sld3.
• DDK promotes replication by phosphorylating MCM, with flexible timing relative to CDK.

Conclusions:

• Defined the minimum protein complement, kinase substrates, and co-factors essential for regulated eukaryotic DNA replication.
• Demonstrated the distinct regulatory roles of CDK and DDK in controlling replication initiation timing and progression.