Distinct functional domains in the cowpea mosaic virus movement protein

Cell-to-cell movement of cowpea mosaic virus particles in plants takes place with the help of tubules that penetrate presumably modified plasmodesmata. These tubules, which are built up by the virus-encoded 48-kDa movement protein (MP), are also formed on single protoplast cells. To determine whether the MP contains different functional domains, the effect of mutations in its coding region was studied. Mutations between amino acids 1 and 313 led to complete abolishment of the tubule-forming capacity, while a deletion in the C-terminal region resulted in tubules that could not take up virus particles. From these observations, it is concluded that the MP contains at least two distinct domains, one that is involved in tubule formation and that spans amino acids 1 and 313 and a second that is probably involved in the incorporation of virus particles in the tubule and that is located in the C terminus between amino acids 314 and 331. Movement of plant viruses from infected cells into adjacent healthy cells is an essential step in the systemic invasion of the whole plant by the virus. For this cell-to-cell movement, plant viruses seem to circumvent the cell wall by exploiting the plas-modesmata (1, 4). At least two different mechanisms for viral cell-to-cell movement via plasmodesmata have been propose