The function of temporally ordered viral gene expression in the intracellular replication of herpes simplex virus type 1 (HSV-1).

In the reproduction of HSV-1, the temporal profile of the viral gene expressions and the molecular mechanisms regulating the expressions are extensively studied. Functional roles of the temporally ordered gene expressions has not yet been clarified. We construct a simple mathematical model for the intracellular replication of HSV-1 to investigate the function of the ordered gene expressions. We obtain the condition for the 'explosion' of the virus from our model. The expression ratio of the early gene to the late gene must be higher than the ratio of the reaction rate of the encapsidation to that of the viral DNA replication for viruses to reproduce successfully. The preceded accumulation of the early gene product prevents the growth arrest. Further, as promoter activity of the early gene becomes higher, the replication speed of virus becomes faster. The structure of early gene promoter that has many binding motif to transcription factor accelerates the replication speed of HSV-1. This structure of the early gene promoter might be selectively maintained by allowing fast growth of the virus. With amino acid limitation, there exist finite optimal ratio of early/late gene promoter activity.