Correct option is C
Explanation-
Role of Cdc45:
1. Initiation: Cdc45 is recruited during the formation of the pre-initiation complex. It associates with the MCM (minichromosome maintenance) helicase complex and GINS complex to form the CMG complex (Cdc45–MCM–GINS), which is the active helicase.
2. Elongation (Replication Fork Progression): Cdc45 remains associated with the replication fork and is essential for the unwinding of DNA during replication. It travels with the replication fork and ensures smooth DNA strand separation as replication proceeds.
Hence, Cdc45 is critical for both in initiation of replication and for sustained progression of the replication fork.
Incorrect options-
Option a – ORC (Origin Recognition Complex)
ORC binds to origins of replication to mark the start sites for DNA replication. It is essential for the initiation phase but not involved once the replication fork starts moving. This is only needed for initiation, not for fork progression.
Option b – Geminin
Geminin is a regulatory protein that prevents DNA from being re-replicated within the same cell cycle. It inhibits Cdt1, a factor required for loading MCM helicases onto DNA. Geminin inhibits replication licensing — it does not help initiate or advance the replication fork.
Option d – Cdc6
Cdc6 works with ORC to help load the MCM helicase onto DNA during the G1 phase (licensing). It is degraded or inactivated after initiation to prevent re-replication. Cdc6 is only involved in initiation (licensing) and is not present during replication fork progression.
Final Answer: Option c – Cdc45
