For initiation of replication and unwinding of DNA double helix, CMG complex of CDC45, MCM2-7 hexamer and the GINS proteins functions as a helicase. The two DNA strands separate and form a replication bubble and the two replication forks move away from the replication bubble. For initiation of DNA synthesis, a RNA primer (6-10 nucleotide) is required, which is synthesized by DNA polymerases alpha:primase. After the synthesis of primer, DNA polymerase synthesizes an additional 20 nucleotides of DNA primer.
