Active intranuclear movement of herpesvirus capsids

Although small molecules diffuse rapidly through the interphase nucleus(1,2), recent reports indicate that nuclear diffusion is limited for particles that are larger than 100 nm in diameter(3). Given the apparent size limits to nuclear diffusion, there is some debate as to whether the movement of large particles should be attributed to diffusion or to active transport(4-6). Here, we show that 125 nm-diameter herpes simplex virus 1 (HSV-1) capsids are actively transported within infected nuclei. Movement is directed, temperature- and energy-dependent, sensitive to the putative myosin inhibitor 2,3-butanedione monoxime (BDM)(7,8) and to actin depolymerization with latrunculin-A, but insensitive to actin depolymerization with cytochalasin-D.