FIGURE 2.

Maturation of α-herpesviral H- and L-particles. Capsids containing viral DNA (1a) are enveloped together with tegument proteins by budding from the inner nuclear membrane resulting in the formation of primary enveloped H-particles (2a). Simultaneously, the budding process can occur with tegument proteins alone in the absence of capsids (1b) resulting in the formation of empty particles within the perinuclear space (2b and 2c). The primary envelope of H-particles fuses with the outer nuclear membrane leading to translocation of the nucleocapsids into the cytosol (3a). L-particles fuse with the outer nuclear membrane (3b) or when migrating through the endoplasmatic reticulum (3c). Nucleocapsids acquire additional tegument proteins and obtain the final envelope by budding into the trans-Golgi network (TGN) (4a). Additionally, L-particles containing tegument proteins (4b) are formed. Some of the L-particles also include inclusion vesicles (IVs) (4c). The origin of IVs can be the endoplasmatic reticulum, membranes of the TGN or other membrane compartments. After secondary envelopment, the H- and L-particles are packed in secretory vesicles (5), transported to the plasma membrane (6) and finally released from the cell (7). The particles released from the infected cell are infectious H-particles (8) and non-infectious L-particles (9), which can additionally contain inclusion vesicles (10).