The movement protein BC1 promotes redirection of the nuclear shuttle protein BV1 of Abutilon mosaic geminivirus to the plasma membrane in fission yeast.

In order to monitor their interaction and cellular localisation, the movement protein (MP; syn. BC1) and the nuclear shuttle protein (NSP; syn. BV1) of the geminivirus Abutilon mosaic virus (AbMV) were ectopically expressed in Schizosaccharomyces pombe cells, either alone or together under the control of an inducible promoter. For highest resolution, electron microscopy using freeze-fracture immunolabelling served to detect these proteins in situ. As expected from previous in planta and yeast experiments, NSP accumulated within the nuclei, whereas MP was targetted to the protoplasmic face of plasma membranes when expressed alone. Upon coexpression, NSP was localised at the plasma membranes, where it was strongly attached. These results support a model in which NSP transports viral DNA to the cell periphery to facilitate cell-to-cell movement of viral DNA within plants. In contrast to AbMV MP, no plant-specific protein seems to be necessary for the translocation of NSP to the plasma membrane.