FIG. 5.

Stability of wt and mutant E2 proteins. COS cells were transfected with a pCG expression vector encoding wt E2 or the 390/388 mutant protein. At 20 h after transfection, protein synthesis was blocked by the addition of 25 μg cycloheximide per ml. Cells were harvested, and the levels of E2 protein after 1 h (lanes 4 and 7) and 2 h (lanes 5 and 8) in the presence of cycloheximide were compared to E2 levels in the absence of cycloheximide (lanes 3 and 6) by Western blotting using a polyclonal antiserum to E2. Lane 1 contained purified E2 protein; lane 2 contained extract from untransfected cells. The calculated half-life of both the wt and the 390/388 mutant protein, based on quantitation of the Western blot, was approximately 50 min.