Fig. 2.

Model of the Eukaryotic Replication Fork. The current model, showing Okazaki fragments at three stages of formation. Next to the MCM helicase, the primase Pol α synthesizes an RNA primer (pink box with lines) and a small amount of DNA, beginning lagging strand synthesis. Replication protein A (RPA) coats the single stranded DNA between the Pol α-catalyzed primers. The next primer has been extended by the lagging strand replisome, represented by Pol δ and PCNA. The third Okazaki fragment has been completely extended, and Okazaki fragment maturation, directed by Pol δ, Fen1, and Lig1, is underway. The leading strand is shown as being copied by Pol ε and PCNA, although Pol δ may be responsible for some leading strand synthesis as well. Several important cofactors are not shown for simplicity. Figure inspired by and adapted from [Burgers 2009].