Question

The S-phase cell cycle kinase S-CDK phosphorylates Cdc6 (which targets Cdc6 for degradation). How does this plus the S-phase regulation of binding help restrict DNA replication to S-phase AND prevent re-initiation?

Answer 1

The CDK or cyclin dependent kinase phosphorylates the cdc6 and degrades it. The CDK cyclin is known for preventing the replication of the DNA to the S-phase and prevents re-initiation. The Cdc6 protein is essential for copying the DNA of the cell before the division of the cell and hence helps with the DNA replication process. It helps with the formation of pre-replication complex. The CDK kinase is known to prevent the re-initiation of the DNA and does so by many mechanisms which includes reducing the activity of Cdc6. When the CDK kinase is presence, it does not allow the Cdc6 to bind to the origin and hence the re-replication is prevented. As the CDK kinase is present, it tends to degrade the Cdc6 and hence it is does not bind to the origin and hence DNA replication cannot be initiated. With the help of the Cdk cyclin, it tends to phosphorylate the proteins which are essential for DNA replication and hence helps in initiating DNA synthesis.