Figure 6

Lagging strand DNA synthesis requires repair of the Okazaki fragments. A.) The T4 RNase H, shown with two hydrated magnesium ions (green) in the active site, is a member of the rad2/FEN-1 family of 5' - 3' exonucleases. The enzyme is responsible for the removal of lagging strand RNA primers and several bases of DNA adjacent to the RNA primer which are synthesized with low fidelity by the gp43 DNA polymerase. B.) The T4 DNA ligase, shown with ATP bound in the active site, repairs nicks present after primer removal and gap synthesis by the DNA polymerase. C.) The T4 RNase H structure has been solved with a pseudo-Y junction DNA substrate. D.) The gp32 single stranded binding protein increases the processivity of the RNase H. The two proteins interact between the C-terminal domain of RNase H and the core domain of gp32 on the 3' arm of the replication fork.