Archaeal and eukaryotic MCM rings sequentially melt DNA for replication initiation.

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• DNA replication initiation requires local DNA melting for helicase access.
• The minichromosome maintenance (MCM) complex is the core helicase engine in eukaryotes and archaea.
• The atomic details of DNA melting by MCM during replication initiation remain unclear.

Purpose of the Study:

• To elucidate the sequential mechanism of DNA melting by the MCM complex.
• To understand the atomic progression from base-paired to melted DNA during replication initiation.
• To investigate the conservation of this mechanism in archaea and eukaryotes.

Main Methods:

• Structural analysis of archaeal MCM complex bound to DNA at various melting stages.
• Biochemical assays monitoring ATP binding and DNA melting.
• Comparative structural analysis of eukaryotic MCM complexes.

Main Results:

• A sequential DNA melting mechanism driven by successive ATP binding at MCM ATPase sites was identified.
• Specific MCM aromatic residues mediate discrete DNA melting steps.
• Eukaryotic MCM complexes adopt distinct conformations, one of which is tuned for DNA melting via equivalent aromatic residues.

Conclusions:

• A universal sequential mechanism for DNA melting by MCM complexes exists in archaea and eukaryotes.
• This mechanism is crucial for initiating DNA replication.
• The findings provide atomic insights into the fundamental process of DNA unwinding.