Once inside cells, intracellular pathogens must hijack cellular machinery to move around. Listeria, for example, makes use of the actin cytoskeleton, whereas adenovirus travels on microtubules; vaccinia virus can do both. So how do retroviruses get about? The foamy virus (a complex animal retroviruses) has been shown to travel from its site of entry to the nucleus via microtubule-organizing centres (MTOCs). Ali Saïb and co-workers now reveal how it does this (see ). They observe that transport of the incoming virus requires microtubules and can be blocked by a dominant negative inhibitor of the retrograde motor cytoplasmic dynein. Furthermore, they find that the Gag protein (a structural component of the viral capsid) is the only viral protein necessary for trafficking, pinning down the region of the protein responsible to a 30-residue coiled-coil motif at the N-terminus. The authors then demonstrate that Gag directly interacts with dynein light chain 8 (LC8) within the dynein motor complex. Finally, they follow the effect of a Gag point mutant that cannot interact with LC8(GagL171G) on the viral life cycle, revealing that this interaction is critical for efficient viral infection. Saïb and co-workers conclude that the cytoplasmic dynein motor transports foamy virus along microtubules,speculating that helical coiled-coil motifs similar to that in Gag might be responsible for interaction of the motor with other cargos.
