DDK regulates replication initiation by controlling the multiplicity of Cdc45-GINS binding to Mcm2-7

Area of Science:

• Molecular Biology
• Biochemistry
• Cell Biology

Background:

• Eukaryotic DNA replication is a fundamental process essential for cell division.
• The activation of Mcm2-7 replicative helicases is a critical, committed step in licensing replication origins.
• Helicase activation involves the formation of Cdc45-Mcm2-7-GINS (CMG) complexes.

Purpose of the Study:

• To elucidate the molecular mechanisms governing CMG complex formation.
• To investigate the role of Dbf4-dependent kinase (DDK) in helicase activation.
• To understand how CMG formation is regulated and its impact on replication origin efficiency.

Main Methods:

• Single-molecule biochemical assays were employed to monitor CMG formation in real-time.
• The study focused on the recruitment dynamics of Cdc45 and GINS to Mcm2-7 complexes.
• Investigated the influence of DDK phosphorylation on Mcm2-7 N-terminal tails.

Main Results:

• CMG formation occurs in two distinct stages: initial recruitment to Mcm2-7 tails forming Cdc45-tail-GINS (CtG) intermediates, followed by inefficient transfer to form CMGs.
• DDK-dependent phosphorylation of Mcm2-7 tails modulates CtG formation.
• Increased CtG multiplicity enhances the frequency of CMG formation, indicating a dose-dependent effect.

Conclusions:

• The study reveals a novel two-stage mechanism for helicase activation, regulated by DDK phosphorylation.
• CtG intermediates act as key modulators, linking DDK activity to CMG formation efficiency.
• These findings provide insights into the control of replication origin efficiency and timing in eukaryotes.