Replication fork components

The RF is a multiprotein complex with helicase and DNA synthesis activities. It is called a fork because the structure resembles a two-pronged fork. The helicase activities unwind DNA in front of the fork to create regions of singled-stranded DNA (ssDNA). The helicase components shown are the minichromosome maintenance (MCM) helicase 2-7 hexamer, CDC45, and associated GINS complex (simplified as a single entity here). The ssDNA is coated in RPA (yellow circles) to keep strands from reannealing. Fork protection complex (FPC) components shown are Timeless (TIM), Tipin (TIPIN), Claspin (CLASPIN), and And1 (AND1). Claspin (MRC1 in yeast) helps connect the leading-strand polymerase epsilon (light blue circle) to the helicase. And1 connects the lagging-strand polymerase alpha (tan circle) to the helicase. Pol-alpha is part of the primase complex, which synthesizes primers (thick tan line) on the lagging strand. These primers allow the polymerase of the main lagging-strand (polymerase delta, light green circle) to start synthesis. The direction of DNA synthesis and RF movement into DNA is indicated by arrows.