Phosphorylation and interaction of the movement and coat proteins of brome mosaic virus in infected barley protoplasts

The 3a movement protein (B3a) of brome mosaic virus (BMV) plays essential roles in the cell-to-cell movement of BMV. B3a is known to bind nucleic acids, to transport RNA to neighbouring cells, and to form tubular structures. Here, we tested the assumption that phosphorylation may be a mechanism that regulates B3a functions and showed that not only B3a but also the coat protein, BCP, was phosphorylated in BMV-infected barley protoplasts. Both BCP and B3a were detected in a complex immunoprecipitated from BMV-infected protoplasts with anti-B3a antiserum, implying an interaction between BCP and B3a.