Fig. 2. A schematic map of the herpes simplex virus type 1 (HSV-1) genome and the transcription pattern of HSV-1 in a productive (lytic) infection and in a latent infection of neurons. The internal repeat section is enlarged for emphasis. During a productive infection, multiple immediate-early (alpha), early (beta), and late (gamma) genes are expressed in a coordinate cascade fashion, although in the diagram only one of these transcripts in shown (ICP0 [shown above as ICP-0] messenger ribonucleic acid (mRNA), which is one of the immediate-early transcripts). During latency, however, only one portion of the HSV-1 genome is transcribed to produce the latency-associated transcripts (LATs). These transcripts overlap with the ICP-0 mRNA, but they are transcribed in the opposite direction and, therefore, referred to as “antisense” transcripts. The true functions of the LATs during HSV-1 neuronal latency remain unclear. (Liesegang TJ: Biology and molecular aspects of herpes simplex and varicella-zoster virus infections. Ophthalmology 99:781, 1992)