DNA polymerase switching and processing of an Okazaki fragment on the lagging strand. (A) as the DNA helicase promotes unwinding at the replication fork, DNA pol delta with RFC and PCNA synthesizes DNA on the leading strand. DNA pol alpha initiates synthesis on the lagging strand by generating an RNA primer (red segment) followed by a short segment of DNA. Then, RFC and PCNA load a second DNA polymerase (delta or epsilon) to continue synthesis of the Okazaki fragment. (B) as DNA pol delta approaches the downstream Okazaki fragment, cleavage by RNase H1 removes the initiator RNA primer leaving a single 5'-ribonucleotide. Then, FEN1/RTH1 removes the 5'-ribonucleotide. The resulting nick is sealed by DNA ligase.
From:R. A. Bambara, R. S. Murante, and L. A. Henricksen (1997) Enzymes and reactions at the eukaryotic DNA replication fork. J. Biol. Chem. 272: 4647-4650.