Two and a half hours after infection with a high dose of different strains of HSV-1 which induce rounding of cells, breakdown of actin containing microfilaments can be observed. At the periphery of the cell, actin containing knob-like protuberances were visible. Later on, actin seems to be located exclusively on the surface of cells. Observations were done by immunofluorescence microscopy, scanning electron-microscopy and immunoperoxidase staining of ultrathin sections. The envelope of HSV appears to be stained by anti-actin. Strain IES produces rounding of cells at a high dose of infection before fusion proceeds at 37 degrees C. Similar alterations were not observed with the fusing strains MP and HFEM. Incubation of infected cells at 39 degrees C revealed strain dependent differences of the fusion activity. At 41 degrees C no "fusion from within" of cells but only rounding was detectable. Application of tunicamycin resulted in complete inhibition of fusion by all strains. The fusion activity of some strains of HSV-1 (ANG, HFEM, and MP) was not inhibited by addition of 2-deoxy-D-glucose and 2-fluoro-deoxy-D-glucose. A variant from strain MP could be isolated, which is sensitive to the effects of 2-deoxy-D-glucose. Inhibitors of processing of glycoproteins did not affect fusion of cells.

In rabbit kidney cells infected with strains of Herpes simplex virus producing either cell-rounding or polycaryocytosis. Vinblastine induced paracrystals. This could be shown by phase-contrast- and electron-microscopy. Infections were done under one-step-growth conditions or at low MOI. 90 per cent noninfected cells contained stress fibers as detected by Servablue R250-staining. Shortly after recruitment into polycaryocytes, stress fibres of normal length appearing in criss-cross arrangement can be seen in the periphery of these cells. Later they polymerize to very long fibers and finally they are partially destroyed. The time of destruction depends on the MOI employed. By using Actinomycin D and/or Cycloheximide as blocking agents, it could be shown that polymerization of microfilaments correlates in time with giant cell formation. In view of the fact that the virus synthesis is accompanied in parallel by a special rearrangement of microfilaments as well as polycaryocytosis, both these processes have to be considered as caused by early (and late ?) protein-synthesis (beta-/gamma-proteins) but not as induced by "very-early" proteins (alpha-proteins).