Isoform VP2 is a structural protein that resides within the core of the capsid surrounded by 72 VP1 pentamers. Following virus endocytosis and trafficking to the endoplasmic reticulum, VP2 and VP3 form oligomers and integrate into the endoplasmic reticulum membrane. Heterooligomer VP2-VP3 may create a viroporin for transporting the viral genome across the endoplasmic reticulum membrane to the cytoplasm. Nuclear entry of the viral DNA involves the selective exposure and importin recognition of VP2 or Vp3 nuclear localization signal (shared C-terminus). Plays a role in virion assembly within the nucleus in particular through a DNA-binding domain located in the C-terminal region. A N-terminal myristoylation suggests a scaffold function for virion assembly. The viral progenies exit the cells by lytic release. Isoform VP2 may repress SP1 activation of the SV40 early promoter, via specific protein-protein and protein-DNA interactions. Isoform VP3 is a structural protein that resides within the core of the capsid surrounded by 72 VP1 pentamers. Following virus entry, VP2 and VP3 form oligomers and integrate into the endoplasmic reticulum membrane. Heterooligomer VP2-VP3 may create a viroporin for transporting the viral genome across the endoplasmic reticulum membrane. Nuclear entry of the viral DNA involves the selective exposure and importin recognition of VP2 or Vp3 nuclear localization signal (shared C-terminus). Isoform VP3 represses SP1 activation of the SV40 early promoter, via specific protein-protein and protein-DNA interactions. SP1 additionally participates in recruiting VP3 to the SV40 minichromosome during SV40 assembly. Isoform VP3 plays a role in virion assembly within the nucleus. May initiate host cell lysis when associated with VP4. Isoform VP4 is a viroporin inducing perforation of cellular membranes to trigger virus progeny release. Forms pores of 3 nm inner diameter. VP4 is expressed about 24 hours after the late structural proteins and is not incorporated into the mature virion. Isoform VP2 forms homooligomers, and heterooligomers with VP3 in the endoplasmic reticulum membrane. Isoform VP2 interacts (via D1 domain) with VP1. Isoform VP3 interacts (via D1 domain) with VP1. VP4 oligomerizes with VP3 in the nucleus. Isoform VP3 (via C-terminus) interacts with host SP1, this is probably also the case for VP2; this interaction represses SP1 activation of the SV40 early promoter and participates in virion assembly. Interacts (via nuclear localization signal) with host importin alpha2-beta heterodimer. Following host cell entry, the virion enters into the endoplasmic reticulum through a calveolar-dependent pathway. Then, isoform VP2 integrates into the endoplasmic reticulum membrane and participates in the translocation of viral DNA to the nucleus. Shortly after synthesis, a nuclear localization signal directs isoform VP2 to the cell nucleus where virion assembly occurs. Following host cell entry, the virion enters into the endoplasmic reticulum through a calveolar-dependent pathway. Then, isoform VP3 integrates into the endoplasmic reticulum membrane and participates in the translocation of viral DNA to the nucleus. Shortly after synthesis, a nuclear localization signal directs isoform VP3 to the cell nucleus where virion assembly occurs. The D1 region of isoform VP2 and isoform VP3 is necessary and sufficient to direct the interaction with VP1. The basic-rich C-terminal region of isoforms VP2 and VP3 is sufficient for DNA-binding and may cause compaction of the DNA. The transmembrane region is only used when isoform VP2 and isoform VP3 form oligomers and integrate into the endoplasmic reticulum membrane. Produced by alternative splicing of the late mRNA (19s mRNA). Produced by alternative initiation at Met-119 of isoform VP2. Produced by alternative initiation at Met-228 of isoform VP2. Belongs to the polyomaviruses capsid protein VP2 family.