Genome replication of Herpes simplex viruses takes place in the nucleus. For this purpose, the viral genome must cross the nuclear envelope (NE). The NE separates the nuclear compartment from the cytosol and possesses unique sieving capabilities: substances which are destined to reside in the nucleus are specifically transported to it while everything else remains excluded. The exchange of substances across the NE is mediated by nuclear pore complexes (NPCs). It remains unclear how viruses overcome the tight NPC permeability barrier to deliver their genome into the nucleus. We set out to elucidate the mechanisms underlying the function of the NPC permeability barrier and to investigate the physical configuration of the transported viral DNA.

The physical configurations of the NPC as well as the transported viral DNA were explored by using the nano-approach atomic force microscopy (AFM). Preliminary experiments indicate that the DNA is translocated as a thread-like structure. Additionally, we could show that a controlled enhancement of the NPC permeability, changes the NPC conformational state by a remarkable deepening of the NPC channel in a concentration dependent manner. NPC deepening was paralleled by an unexpected dissociation of NPC proteins as shown for Nup62 and Nup98. At the same time NPCs rendered leaky to large intranuclear proteins. It is presumed that a dissociation of NPC proteins is prerequisite to break down the NPC permeability barrier. It remains to be explored whether Herpes simplex viruses dissociate NPC proteins to deliver their genome through the NPC.