Maize streak virus coat protein binds single- and double-stranded DNA in vitro

Maize streak virus (MSV) coat protein (CP) is required for virus movement within the plant. Deletion or mutation of MSV CP does not prevent virus replication in single cells or protoplasts but leads to a loss of infectivity in the inoculated plant. The mechanism by which MSV CP mediates the transfer of MSV DNA from cell to cell and through the vascular bundle is still unknown. Towards understanding the role of MSV CP in virus movement, the interaction of the CP with viral DNA was investigated using the 'south-western' assay. Wild-type and truncated MSV CPs were expressed in E. coli and the expressed CPs were used to investigate interactions with single-stranded (ss) and double-stranded (ds) DNA. The results showed that MSV CP bound ss and ds viral and plasmid DNA in a sequence non-specific manner. The binding domain was mapped to within the 104 N-terminal amino acids of the MSV CP. We propose that the binding of CP to MSV DNA is involved in viral DNA nuclear transport as well as encapsidation and thus may have a role in intra- and inter-cellular movement as well as systemic infection.