Origin licensing in G1 involves ORC binding and loading of the MCM helicase with which factors?

Origin licensing in G1 involves ORC binding and loading of the MCM helicase with which factors?

• A. Cdc45 and GINS
• B. ORC binding and loading of MCM helicase with Cdc6 and Cdt1
• C. DPB and PCNA
• D. ATR and ATM

Answer: (B)

Origin licensing in G1 centers on assembling the pre-replication complex at each origin. ORC binds the origin and recruits two licensing factors, Cdc6 and Cdt1, which together load the MCM2-7 helicase onto DNA to form the pre-replicative complex. This loading step places MCM in an inactive form until S-phase activation. That’s why the option describing ORC binding and loading of the MCM helicase with Cdc6 and Cdt1 is correct. The other items involve factors that act later in replication or in checkpoints (for example, Cdc45 and GINS are part of the active CMG helicase during firing; DPB and PCNA are downstream replication proteins; ATR and ATM are checkpoint kinases), not the licensing process itself.

Origin licensing in G1 centers on assembling the pre-replication complex at each origin. ORC binds the origin and recruits two licensing factors, Cdc6 and Cdt1, which together load the MCM2-7 helicase onto DNA to form the pre-replicative complex. This loading step places MCM in an inactive form until S-phase activation. That’s why the option describing ORC binding and loading of the MCM helicase with Cdc6 and Cdt1 is correct. The other items involve factors that act later in replication or in checkpoints (for example, Cdc45 and GINS are part of the active CMG helicase during firing; DPB and PCNA are downstream replication proteins; ATR and ATM are checkpoint kinases), not the licensing process itself.