Figure 3. Overexpression of cyclin B1 in synchronized cells induces cell death in G1 phase independent of mitotic arrest.

HeLa cells were synchronized at the G1/S boundary using double thymidine block, released into fresh media, and 1 h post-release were untreated (vehicle), treated with 30 nM vinblastine, or transfected with 2 µg plasmids encoding either GFP vector, wild-type cyclin B1-GFP or cylcin B1-R42A-GFP. Cells were harvested at intervals 10–24 h post-release and extracts subjected to immunoblotting for the indicated proteins. Top panel, experimental scheme, with corresponding cell cycle phases indicated. Bottom panel, immunoblots.