Use of the Herpes Simplex Viral Genome to Construct Gene Therapy Vectors

Fig. 1.  A. Schematic depiction of a mature HSV virion illustrating the main components of the virus particle. B. The HSV genome is organized into unique long and short segments (UL, US) flanked by repeated sequences. The 84 viral open reading frames can be divided into genes that are essential for replication in a permissive tissue culture environment, and those that are dispensable. The functions of the nonessential gene products are related to viral interactions with the host in vivo.

1.	A trilaminar lipid envelope, in which are embedded 10 viral glycoproteins-these are responsible for several functions including receptor-mediated cellular entry (2 –5 ).
2.	A matrix of proteins, the tegument, which form a layer between the envelope and the underlying capsid. Functions of the tegument proteins include: induction of viral gene expression (6 –8 ); shutoff of host protein synthesis immediately following infection (9 –12 ); virion assembly functions.
3.	An icosadeltahedral capsid, typical of the herpesvirus family (13 ,14 ).
4.	A core of toroidal double-stranded DNA (dsDNA) (14 –16 ).