Western blot of PARP proteolysis on treatment of Molt-4 cells with GW1843. Molt-4 cells in log-phase growth were treated with 8 nmol/L GW1843 and aliquots of 2 × 10⁶ cells were taken at the indicated times. Cells were prepared for electrophoresis, electrophoresed on 7.5% polyacrylamide SDS gels,29 and blotted onto nitrocellulose as described in Materials and Methods. The blot is an x-ray film image of PARP protein detected with a horseradish peroxidase-conjugated secondary antibody visualized with chemiluminescent substrate (Amersham) blotted as described in Materials and Methods. The M_r values were determined by running prestained M_r markers (BioRad). Intact PARP (upper band) is M_r 116,000 and the proteolytic fragment is M_r 85,000. This blot is from a representative experiment from four separate determinations.