Interaction between yeast Cdc6 protein and B-type cyclin/Cdc28 kinases

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Cdc6 is essential for DNA replication initiation in eukaryotic cells.
• Cdc28 is the primary cyclin-dependent kinase regulating the cell cycle in yeast.
• Understanding protein interactions is key to deciphering cell cycle control.

Purpose of the Study:

• To investigate the interaction between Cdc6 and Cdc28.
• To elucidate the functional significance of the Cdc6-Cdc28 interaction in cell cycle regulation.
• To determine the role of this interaction in DNA replication and mitosis.

Main Methods:

• Co-immunoprecipitation assays to confirm protein-protein interaction.
• Affinity chromatography using purified proteins to study binding.
• In vitro kinase assays to assess substrate and inhibitor roles.
• Site-directed mutagenesis to identify interaction domains.

Main Results:

• Cdc6 and Cdc28 were found to co-immunoprecipitate and bind to each other's affinity matrices.
• Cdc6 is a phosphoprotein and a substrate of Cdc28 kinase in vitro, and it inhibits Cdc28 kinase activity.
• Cdc6 preferentially interacts with B-type cyclin/Cdc28 complexes, and this interaction is inhibited by p40Sic1.
• Deletion of the Cdc28 interaction domain in Cdc6 impairs its essential function but allows growth upon overproduction, unlike wild-type Cdc6.

Conclusions:

• The interaction between Cdc6 and Cdc28 is essential for the proper function of Cdc6 in initiating DNA replication.
• This interaction plays a role in restraining mitosis until DNA replication is complete.
• The findings suggest a regulatory mechanism involving Cdc6, Cdc28, and Sic1 in cell cycle progression.