Levels of the p53-responsive gene product MDM2 following treatment of REF and REF lines expressing wild-type T antigen (T1-708), N-terminal fragment T1-127, or C-terminal fragment T251-708. REF or REF lines expressing the T antigens indicated were either treated overnight with 10 μM 5-FU (5-FU) or left untreated (UT). Protein extracts were prepared, and MDM2 was immunoprecipitated from 300 μg of lysate by using Ab-2. Immunoprecipitates were subjected to SDS- 10% PAGE, proteins were transferred to PVDF membranes, and MDM2 was detected by using Ab-1. The migration positions of the MDM2 proteins are indicated.