Herpes simplex virus products in productive and abortive infection. 3. Differentiation of infectious virus derived from nucleus and cytoplasm with respect to stability and size.

Approximately 67% of infectivity is associated with the nucleus 8 hr after productive infection of HEp-2 cells with herpes simplex virus. Comparison of nuclear and cytoplasmic infectious virus and macromolecular aggregates labeled with (3)H-thymidine or with (3)H-choline revealed the following. (i) Cytoplasmic infectious virus and macromolecular aggregates banded in CsCl at a density corresponding to enveloped nucleocapsids. The virus was relatively stable; there was only 50% loss of infectivity and only 16% of the virions became disaggregated. (ii) Nuclear macromolecular aggregates banded in CsCl solution at a density corresponding to unenveloped nucleocapsids and, moreover, both the infectious virus and aggregates were highly unstable. (iii) In sucrose density gradients, the nuclear macromolecular aggregates and infectivity sedimented as a single band and migrated more slowly than the corresponding cytoplasmic material. (iv) The infectivity of nuclear and cytoplasmic virus is readily inactivated by digestion with phospholipase C and with pronase. We conclude the following. (i) Cytoplasmic virus consists of enveloped nucleocapsids. (ii) Nuclear virus consists of nucleocapsids covered with lipid or partially enveloped. (iii) The molecular integrity of viral lipids is essential for infectivity. (iv) The envelope protects the nucleocapsid and accelerates adsorption to cells; it is not, however, inherently essential for infectivity.