Interaction of the movement and coat proteins of Maize streak virus: implications for the transport of viral DNA

We have shown previously that the movement protein (MP) and coat protein (C P) of Maize streak virus (MSV) are both required for systemic infection. To wards understanding the roles of these two protei ns in virus movement, eac h was expressed in E. coli and interactions of the MP with viral DNA or CP were investigated using south-western, get overlay and immunoprecipitation assays. Unlike the CP, the MP did not bind to viral DNA but it interacted w ith the CP in vitro and an MP-CP complex was detected in extracts from MSV- infected maize, indicating the potential for an interaction in vivo. Microi njection showed that the MP could prevent the nuclear transport of an MSV C P-DNA complex in maize and tobacco cells. These results are consistent with a model in which the MP diverts a CP-DNA complex from the nucleus (where v iral DNA replication takes place) to the cell periphery, and in co-operatio n with the CP, mediates the cell-to-cell movement of the viral DNA. In this respect, the MSV MP and CP have functional analogy with the BC1 and BV1 pr oteins, respectively, of the Begomovirus genus of the Geminiviridae.