HT1080 cells were transfected with each fusion protein or PACT construct and stressed with actinomycin D. Although MBP-3 and wtPACT each can homodimerize and activate PKR, only wt PACT contains a strong PKR-binding domain. Immunofluorescence assays were performed to detect cells expressing protein from the transfected constructs, which were scored for apoptosis using TUNEL assay. For each transfection, panels show independent photographs of the same cells, with different filters, to indicate nuclei (DAPI), cells undergoing apoptosis (TUNEL), and fusion protein or PACT-expressing cells (IF). MBP, maltose binding protein; MBP-3, maltose binding protein fused to PACT domain 3. The TUNEL results are representative of three independent experiments.