DNA ligase
Further research implicates the supplementary role of proliferating cell nuclear antigen (PCNA) to DNA ligase I's function of joining Okazaki fragments. When the PCNA binding site on DNA ligase I is inactive, DNA ligase I's ability to connect Okazaki fragments is severely impaired. Thus, a proposed mechanism follows: after a PCNA-DNA polymerase δ complex synthesizes Okazaki fragments, the DNA polymerase δ is released. Then, DNA ligase I binds to the PCNA, which is clamped to the nicks of the lagging strand, and catalyzes the formation of phosphodiester bonds.