Scission of the filamentous virus particle from the PM then takes place with a bud-neck shape which can have a circular cross-section. This is the same shape as the bud-neck which would be present in the budding of spherical enveloped virions, or in the budding of vesicles into a multi-vesicular body [40] . Release of a horizontally budding particle would require scission of a membrane neck with a noncircular cross-section. Our observations indicate that no such unusual scission mechanism needs to be proposed.