Cytochemical analysis of DNA organization during encapsidation in herpes simplex virus

The organization of intranuclear Herpes simplex virus DNA in rabbit fibroblast cells infected for 7 hr with HSV type 1 was examined before and during encapsidation by electron microscopic cytochemistry. Most non-encapsidated viral deoxyribonucleoprotein fibers exhibited a non-nucleosomal configuration. Empty capsids within the virus-specific regions of infected nuclei were wrapped with portions of the viral genome which adhered tightly to their surfaces even under conditions that loosened and spread apart other nucleoprotein fibers. During encapsidation, the internal surface of the capsid shell also appeared to bind a part of the viral genome, specifically the outer cage portion, which is detectable in methanol-dehydrated cells. Variations in the amount of DNA within the capsids indicated that the insertion of HSV genome into the capsid is a progressive process. The cage and core cylinder portions of the viral nucleoid appear to form and develop simultaneously. We propose that there may be binding sites on both the external and internal surfaces of the capsid shells which might play a role in the encapsidation process.