The key event in controlling replication is the behavior of the ORC complex at the origin.

Cdc6 protein is an unstable protein that is synthesized only in G1.

Cdc6 binds to ORC and allows MCM proteins.

Cdc6 binds to ORC and allows MCM proteins to bind.

Cdt1 facilitates MCM loading on origins

TLS Online TPP Program

#Id: 6015

#Unit 3. Fundamental Processes

The origin enters S phase in the condition of a prereplication complex, which contains ORC, Cdc6, Cdt1, and the inactive helicase

TLS Online TPP Program

#Id: 6016

#Unit 3. Fundamental Processes

The MCM2-7 proteins form a six-member ring-shaped complex around DNA. MCM2,3,5 are regulatory, while MCM4,6,7 have the helicase activity.

TLS Online TPP Program

#Id: 6017

#Unit 3. Fundamental Processes

In mammalian cells, Cdt1 is targeted for degradation by the action of a protein complex that is recruited to the origin of replication by PCNA, the eukaryotic counterpart of the bacterial b clamp.

TLS Online TPP Program

#Id: 6018

#Unit 3. Fundamental Processes

As the transition from G1 to S phase begins, CDK/cyclins recruit cdc45 and the GINS complex to the MCM helicase, which then becomes known as the CMG complex (Cdc45-MCM-GINS)

TLS Online TPP Program

#Id: 6019

#Unit 3. Fundamental Processes

TLS Online TPP Program

#Id: 6020

#Unit 3. Fundamental Processes

As cells enter into the S phase of the cell cycle, two kinases, CDK and DDK, are activated.  DDK phosphorylates loaded Mcm2-7 helicase, and CDK phosphorylates Sld2 and Sld3.Phosphorylated Sld2 and Sld3 bind to Dpb11, and together these proteins facilitate binding of the helicase-activating proteins, Cdc45 and GINS, to the helicase.