Comparative Roles of Herpes Simplex Virus Type 1 (HSV-1) Glycoproteins in Cytoplasmic Virion Egress

by Lee, HyunCheol

HSV-1 acquires its final envelope by budding into cytoplasmic vesicles thought to be derived from Trans-Golgi Network (TGN) membranes. This process is facilitated by interactions among the carboxyl termini of viral glycoproteins and tegument proteins. To investigate the relative importance of different viral glycoproteins in cytoplasmic virion morphogenesis, a set of recombinant viruses were constructed silencing expression of the glycoprotein E (?gE), the carboxyl terminus of glycoprotein D (gD?cp), and the membrane protein UL20 (?UL20). In addition, recombinant viruses were constructed having the ?gE+gD?cp, and the ?gE+?gM (glycoprotein M) deletions. These recombinant viruses were constructed using the double-red, site-directed mutagenesis system implemented on the HSV-1 genome cloned into a bacterial artificial chromosome (bac). The ?gE, ?gE+?gM, and gD?cp viruses produced viral plaques that were approximately 50% smaller to those produced by the wild-type virus HSV-1(F strain). The gD?cp+?gE recombinant virus produced viral plaques that were on the average 50% smaller to those produced by either the ?gE, ?gE+?gM, or the gD?cp viruses. However, these viral plaques were substantially larger than those produced by previously constructed UL20-null or gK-null viruses. Kinetics of viral replication revealed that all recombinant viruses appeared to produce similar viral titers at late times post infection. However, both the gD?cp and the ?gE+gD?cp viruses appeared to replicate slower than the wild-type virus or the ?gE and ?gE+?gM viruses. Electron microscopy revealed that all viruses regardless of their different gene mutations produced enveloped virions that were secreted outside, with no apparent accumulation of unenveloped capsids in the cytoplasm of infected cells. These results suggest that the gD and gE carboxyl termini, either alone or in a redundant manner, are not essential in cytoplasmic virion envelopment and egress from infected cells. Furthermore, the results show that gK/UL20 complex serves preeminent roles among all viral glycoproteins in cytoplasmic virion morphogenesis and egress.