Electron tomography studies of MARV-infected cells led to the following model for MARV particle release: The budding process is initiated when intracellular nucleocapsids associate laterally with the plasma membrane. Starting from one end, the nucleocapsids are then subsequently wrapped by the plasma membrane until the viral particles protrude vertically from the cell surface. The release of infectious filamentous MARV from cultured cells peaked at 1-2 days post infection, when the cells were still intact. At 4 d post infection, when most of the cells were vesiculated, the released virions were round or bent and infectivity was decreased [189] . Determination of the nucleocapsid orientation at the sites of budding by 3-D reconstructions revealed that the pointed tip of the budding nucleocapsids is oriented towards the membrane, indicating that MARV budding is directional [60] .