Interaction of the adenovirus major core protein precursor, pVII, with the viral DNA packaging machinery

Adenovirus is one of the well-studied double-stranded DNA viruses. However, the mechanisms of its DNA packaging and virion assembly are still not fully understood. One of the unique features of adenovirus is that the unpackaged viral DNA is associated with core protein pVII. Packaging of viral DNA bound with proteins has not been reported from other viruses. To characterize how viral DNA bound with protein pVII is packaged, we performed experiments to see if protein pVII interacts with the known DNA packaging proteins or the packaging sequence. Our results demonstrated that protein pVII interacted with the viral IVa2 and L1 52/55 kDa proteins, which are the known viral DNA packaging proteins. Furthermore, our protein-DNA binding experiments demonstrated that the IVa2 protein mediates the specific interaction with the packaging sequence, whereas protein pVII and the L1 52/55 kDa protein bind to DNA non-specifically. Although the non-specific binding of protein pVII and the L1 52/55 kDa protein do not appear to affect the specific binding of the IVa2 protein to the packaging sequence, and the specific binding of the IVa2 protein does not appear to block the bindings of protein pVII and the L1 52/55 kDa protein to the packaging sequence, the possibility of a cooperative binding among the IVa2 protein, the L1 52/55 kDa protein and protein pVII on the packaging sequence needs to be further determined. In summary, the results indicate that the assembly of the DNA packaging initiation complex may be mediated by the specific interaction of the IVa2 protein with the packaging sequence and other viral proteins, such as protein pVII and the L1 52/55 kDa protein.