Co-occupancy of TopBP1, E2F1, and Brg1/Brm on E2F1-responsive promoters. (A) HEK293 cells were transfected with an empty vector or a TopBP1-expressing plasmid. Some empty-vector-transfected cells were treated with NCS (300 ng/mL) for 3 h. A chromatin immunoprecipitation (ChIP) assay was performed using antibodies against E2F1, TopBP1, Brm, or Brg1, respectively, as indicated. Mock immunoprecipitations correspond to control reactions lacking antibodies. The IgG lane represents an additional control reaction using normal mouse IgG for chromatin immunoprecipitation. The precipitated DNA was amplified with two primers derived from an E2F1 promoter or a β-actin promoter. The input represented 0.5% of total amount of chromatin added to each immunoprecipitation reaction. (B) T98G cells were transfected with an empty vector or a TopBP1-expressing plasmid. Some empty-vector-transfected cells were treated with NCS (300 ng/mL) for 3 h. ChIP was performed as above. The precipitated DNA was amplified with primer pairs derived from each promoter as indicated. A longer exposure of p73 promoter ChIP assay is shown to demonstrate the occupancy of Brm.