Figure 8.

Schematic representation of the nuclear import pathway for the PRV DNA polymerase holoenzyme. (A) UL30 is not independently transported into the nucleus because it is large (116 kDa) and lacks a functional NLS. (B) UL42 can be independently imported into the nucleus via the classical importin α/β pathway. First, UL42 binds to the importin α/β heterodimer via its bipartite NLS to form a heterotrimeric complex in the cytoplasm, which then binds to the NPC via importin β. Second, the complex is translocated into the nucleus, where UL42 is released from the complex when importin β binds to nuclear RanGTP, and the transport receptors importins α and β are then recycled back to the cytoplasm for another round of import. (C) Nuclear import of the PRV DNA polymerase holoenzyme relies on the bipartite NLS present in its accessory subunit UL42. The UL42/UL30 holoenzyme complex was first assembled in the cytoplasm and then transported into the nucleus by the importin α/β pathway.