Fig. (1) Schematic representation of the HSV-1 genome. The HSV-1 genome is a linear double stranded DNA of approximately 152 kb in size, composed of two unique segments, U_L and U_S, which are flanked by inverted repeats, TR_L /IR_L and IR_S/TR_S. The minimal cis elements required for HSV-1 DNA replication and packaging include the origin of DNA replication, ori, and the cleavage/packaging, pac, signals.