Background：

As a component of the trimeric and tetrameric DNA polymerase delta complexes (Pol-delta3 and Pol-delta4， respectively)， plays a role in high fidelity genome replication， including in lagging strand synthesis， and repair. Required for optimal Pol-delta activity. Stabilizes the Pol-delta complex and plays a major role in Pol-delta stimulation by PCNA. Pol-delta3 and Pol-delta4 are characterized by the absence or the presence of POLD4. They exhibit differences in catalytic activity. Most notably， Pol-delta3 shows higher proofreading activity than Pol-delta4. Although both Pol-delta3 and Pol-delta4 process Okazaki fragments in vitro， Pol-delta3 may also be better suited to fulfill this task， exhibiting near-absence of strand displacement activity compared to Pol-delta4 and stalling on encounter with the 5’-blocking oligonucleotides. Pol-delta3 idling process may avoid the formation of a gap， while maintaining a nick that can be readily ligated. Along with DNA polymerase kappa， DNA polymerase d