A Positive Amplification Mechanism Involving a Kinase and Replication Initiation Factor Helps Assemble the...

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• DNA replication initiation in eukaryotes involves the assembly of the replication fork helicase.
• Key steps include the association of Cdc45 and the GINS complex with the Mcm2-7 heterohexamer.
• The precise roles of initiation factors like Dpb11, DDK, and S-CDK in helicase assembly are not fully understood.

Purpose of the Study:

• To elucidate the role of Dpb11 in the assembly of the replication fork helicase.
• To investigate the interaction between Dpb11, DDK, and Mcm2-7 complex components.
• To understand the mechanism of GINS complex recruitment during replication initiation.

Main Methods:

• In vitro phosphorylation assays to assess Dpb11's effect on DDK activity.
• Binding assays to determine protein-protein interactions.
• Site-directed mutagenesis to create phosphomimetic and binding-defective mutants.
• Analysis of budding yeast mutants for cell growth, DNA replication, and protein complex assembly.

Main Results:

• Dpb11 stimulates DDK phosphorylation of Mcm4 and the Mcm2-7 complex.
• Dpb11 directly recruits DDK to Mcm4.
• A DDK phosphomimetic Mcm4 mutant enhances Dpb11 binding, suggesting a recruitment mechanism.
• dsDNA-loaded Mcm2-7 with the phosphomimetic Mcm4 mutant binds GINS in the presence of Dpb11.
• A Dpb11 mutant defective in Mcm4 binding impairs cell growth, DNA replication, Mcm4 phosphorylation, and GINS association with origins.

Conclusions:

• Dpb11, DDK, and Mcm4 function in a positive feedback loop to initiate replication fork helicase assembly.
• Dpb11 acts as a scaffold, recruiting DDK to Mcm4 and facilitating GINS recruitment.
• This mechanism amplifies the initiation signal for DNA replication.