▪ Abstract Because many viruses replicate in the nucleus of their host cells, they must have ways of transporting their genome and other components into and out of this compartment. However, their exact function during viral replication is unknown. Using GFP-tagged capsids, Cy3-labelled MT and cytosol, we have reconstituted viral capsid transport in vitro. Using an HSV-1 variant containing a functional hemagglutinin-tagged UL32, we demonstrated that UL32 was synthesized with true late kinetics and that it exhibited a previously unrecognized localization pattern. Marker rescue of tsB7 by transfection with herpes simplex virus 2 XbaI DNA fragments mapped the mutation between 0.45 and 0.70 map units. After the capsid is transported along the microtubule to the microtubule-organizing center, it migrates by an unknown mechanism to the edge of the cell nucleus, where it interacts with the nuclear pore, releasing the viral genome into the nucleus by a process dependent on importin-β and Ran-GTP (3, 29, 38, 51). These include SV40, BK, JC and polyoma viruses.
Nonetheless, it also showed that HSV1 capsids possess a remarkable structural integrity that was preserved after removal of pentons. Subsequent analysis of the latter classes of mutant proteins demonstrated that one class enabled the null virus to release enveloped virus particles from U2OS cells, whereas the other class prevented egress of mature HSV-1 capsids from the nucleus.