Identification of a nuclear protein that binds to p53 binding sites. (A) Binding of p53CP to T3SF and (B) binding of p53CP to Gadd45, Waf1, and p53CON. The nuclear extract was prepared from H-Tx mouse liver tumor cells and subjected to gel retardation assay with a poly(I/dC) concentration of 10 μg/ml. In some reactions, p53 antibody, pAb421 was included. The oligo nucleotides used were the following: T3 5′-AGGGCTTGCTTGACGTCCAGAACAGGGTCT-3′, the sequence found in the promoter of mouse TIMP-3; T3SF 5′-AGGGCTTGCTTGAACAGGGTCT-3′; T3MD 5′-AGGGCTTGCTTGACGTCCAGGTCT-3′; GADD 5′-GAACATGTCTAAGCATGCTG-3′; WAF 5′-GAACATGTCCCAACATGTTG-3′; and p53CON 5′-AGACATGCCTAGACATGCCT-3′. The protein complexes bound to T3 oligonucleotide are indicated by arrows. Also indicated are p53-Ab complex, p53CP (band 3), and free probe.