Expression of the tomato ringsport nepovirus movement and coat proteins in protoplasts.

Tomato ringspot nepovirus (TomRSV) produces a 45 kDa movement protein and a 58 kDa coat protein in infected plants. Accumulation of the movement protein in relation to that of the coat protein was studied in infected protoplasts using a monoclonal antibody against the movement protein and polyclonal antibodies against the coat protein. Unlike most other viral movement proteins, the TomRSV movement protein was present at late stages of infection. Pulse-chase labelling experiments revealed that the release of the movement protein from the precursor polyprotein was coordinated with that of the coat protein. However, the movement protein was less stable than the coat protein in the extractable fraction of the protoplasts. The expression pattern of the TomRSV movement protein is discussed in the light of the proposed mechanism of cell-to-cell movement of virus-like particles through tubular structures composed of the movement protein.