Alters the structure of the nuclear envelope. Involved in the perinuclear-nuclear localization of the capsid protein VP1 during virion assembly and maturation. May contribute to viral genome transcription and translation of viral late proteins. Plays an important role in the release of progeny virions from infected cells and in viral propagation (By similarity). Interacts with VP1. Interacts with Large T antigen. Interacts with small t antigen. Phosphorylated by host PKC. Phosphorylation alters the stability and may also have an impact on the subcellular location (By similarity). Produced by alternative initiation of the late mRNA. Encoded by the same late mRNA leader region, but very different from other primate polyomavirus agnoproteins.