p65-p53 complexes are associated with the inactive MDM2 promoter in HTLV-I–transformed cells. Following treatment of Hut102 and Molt4 cells with 8 Gy ionizing radiation (IR), total RNA (A) was extracted from time 0 (–) or 4 hours after irradiation (+) with use of RNA-Bee (TelTest) as described by the manufacturer. Total RNA (2 μg) was then subjected to reverse transcription and PCR, as described in “Materials and methods,” for amplification of MDM2 or GAPDH mRNA. Reactions were run on 2% agarose gels to visualize the products. (B) Chromatin immunoprecipitation (ChIP) assays were performed on untreated Hut102 cells or Molt4 cells treated with 8 Gy ioinizing radiation (Molt4-IR) with use of the indicated antibodies. PCR amplification was performed with primers specific for the MDM2 promoter. (C) ChIP assays were performed on Hut102 cells to determine the association of p65 and p53 on the MDM2 promoter. Samples were immunoprecipitated with either control IgG sera or anti-p53 or anti-p65 sera (lanes 2, 3, and 5, respectively). Supernatants from anti-p53 and anti-p65 precipitations were then subjected to a second round of precipitation with the anti-p65 or anti-p53 sera, respectively (lanes 4 and 6). DNA was then PCR amplified with primers specific for the MDM2 promoter.