(A) Schematic representation of the amino acid sequences of PML/RARα and mutants. P, proline-rich region; R, RING finger domain; B1 and B2, B-boxes; C.C., coiled-coil region; α-H, α-helix region; SP, the α-helix serine and proline-rich region; BP, PML/RARα junction. (B through F) RARα functional regions. (B) MBP-PML/RARα (MBP-P/R) or (C) in vitro–translated [³⁵S]-PML/RARα (P/R) or (D) [³⁵S]-▵C P/R, (E) [³⁵S]-▵H P/R, and (F) [³⁵S]-H4-RAR were incubated with GST or GST caspase 3 for 1 hour at 37°C. One hundred micromoles per liter DEVD was added where indicated. Samples were analyzed by discontinous 8% to 15% SDS-PAGE and visualized by autoradiography or by immunoblotting (B) using an anti-RARα antibody (Santa Cruz Biotechnology). Molecular weight markers are indicated. Arrows indicate the p50 proteolytic fragment.