FIG. 7.

HSV entry is independent of the ubiquitin-activating enzyme, E1. ts20 or BALB/c 3T3 cells were cultured at 35 or 39°C for 18 h. (A) p53 is not degraded in ts20 cells at the nonpermissive temperature. Lysates were prepared and analyzed by SDS-polyacrylamide gel electrophoresis and immunoblotted for p53 or α-tubulin (Tub). (B and C) HSV infects cells with an inactive polyubiquitination machinery. HSV-1 KOS-tk12 was added to cells cultured at 35°C (B) or 39°C (C). The β-galactosidase activity was determined at 6 h p.i. (D to E) Ubiquitin-independent entry of HSV requires proteasome activity. ts20 cells maintained at 39°C were treated with MG132 (D) or lactacystin (E) for 15 min. HSV-1 KOS-tk12 was added in the presence of inhibitor. The β-galactosidase activity was measured at 6 h p.i. (as in Fig. 1). The data are means of quadruplicate determinations with the standard errors.