Latent herpes simplex virus type 1 DNA is not extensively methylated in vivo.

The methylation pattern of herpes simplex virus type 1 (HSV-1) DNA, present in the central nervous system of latently infected mice, was examined by digestion of the DNA with methylation-sensitive restriction endonucleases and Southern blot hybridization. Using the enzymes SmaI, XmaI, SalI and SacII, the data indicate no extensive methylation of latent HSV-1 DNA in vivo. Thus, extensive methylation of the viral genome is not a necessary condition for, or a consequence of maintaining, the latent state in vivo.