Two populations of herpes virus virions which appear to differ in physical properties and DNA composition.

Abstract

HEp-2 cells infected with herpes simplex virus give rise to two kinds of progeny virions which can be separated by rate zonal centrifugation in linear sucrose gradients. The more slowly sedimenting E virions contain most of the infectivity and have a buoyant density of 1.262 gm/cm3. The more rapidly sedimenting G virions are more numerous but farless infectious. Although morphologically indistinguishable from the E virions, the G virions appear to differ in the following surface properties: they are more heat-labile, less readily neutralized by antibody, and have a lower buoyant density of 1.254 gm/cm3. DNA extracted from E virions proved to be a single species with a density of 1.720 gm/cm3, which is characteristic of herpes virus DNA. By comparison, G virions were found to contain H3-thymidine label in DNA of three different densities: viral DNA of density 1.720 gm/cm3, cellular DNA of density 1.680 gm/cm3, and an unidentified DNA (or nucleoprotein) of density 1.645 gm/cm3, which is cellular in origin but found only after HSV infection. The G virions, of low infectivity, probably represent a heterogeneous population which vary in their content of viral and cellular DNA. Chase experiments revealed that an appreciable number of HSV virions are associated with preformed cellular DNA which is presumably fragmented during infection and is firmly bound to or packaged in capsids. The cellular DNA of very low density that appears during infection is apparently not packaged and can be separated from the G virions by equilibrium sedimentation in CsCl, particularly at high salt concentration. Further studies are required to prove that cellular DNA is packaged in herpes virions.