Nucleocapsid protein that mediates the translocation of G-actin from the host cytoplasm to the nucleus, which is fundamental to infection. Participates in regulating nuclear actin polymerization as well as the morphogenesis and spatial distribution of viral capsid structures in the host nucleus. Suppresses 'Lys-48'-linked ubiquitination of the viral protein C42, thus forming a regulatory cascade with C42 to control P78/83 availability as an nucleation promoting factor (NPF). Interacts with protein C42; this interaction suppresses C42 'Lys-48'-linked-ubiquitination and subsequent proteasomal degradation. Interacts with proteins P78/83 AND E27.