Figure 1. The structure and mechanisms of a herpes simplex virus.

(A) Cryo-electron microscopy images of a herpes simplex virus (left) and a section through a three-dimensional reconstruction of the viral capsid (right). Herpesviruses consist of a protective capsid containing the viral DNA, and a tegument layer connecting the capsid and the membrane envelope surrounding the virus. Two subunits, hexon and penton, are located at the icosahedral vertices of the capsid, where three proteins (pUL17, pUL25, pUL36 – the latter is not visible on the map) form a complex that anchors the tegument layer to the capsid. Scale bars shown on lower left of each image represent 50 nanometers. (B) Schematic representation showing entry of the herpes virus into cells, following the fusion of the viral envelope with the host cell membrane. Once inside the cell, the capsid (blue hexagon) and its associated tegument proteins (shaded blue ring) traffic to the nucleus along microtubules, and dock at the pores of the cell nucleus to release the viral genome (black lines). The interferon-induced protein MxB (green) can only attach to the capsid when the tegument is absent (light blue shading) and divert the viral genome into the host’s cytoplasm by seemingly punching holes into the vertices of the capsid. The exposed viral genome may alert defense proteins to activate an anti-viral response.