Plays an essential role in viral DNA replication by acting as the polymerase processivity factor together with protein D4. May serve as a bridge which links the DNA polymerase E9 and the uracil DNA glycosylase (By similarity). Interacts with the DNA polymerase catalytic subunit E9. Interacts with UDG. Component of the Uracil-DNA glycosylase(UDG)-A20-polymerase complex; A20 and UDG form a heterodimeric processivity factor that associates with E9 to form the processive polymerase holoenzyme. Interacts with D5 (By similarity). Belongs to the poxviruses A20 family.