Self-assembles to form the virion icosahedral capsid with a T=1 symmetry. This very small capsid (17-22 nm in diameter) allows the virus to be very stable in the environment and resistant to some disinfectants, including detergents. Essential for the initial attachment to heparan sulfate moieties and chondroitin sulfate B of the host cell surface proteoglycans. After attachment, the virus is endocytosed and traffics to the nucleus. The capsid protein binds and transports the viral genome and Rep across the nuclear envelope. Homomultimer. Assembles in the nucleus, presumably in an immature form, then migrates to the cytoplasm once assembled as mature virion. Interacts with Rep; this interaction relocates Rep into the nucleus. Belongs to the circoviridae capsid protein family.