FIG. 1.

ORF50 represses p53-induced transactivation. (A) The domains within ORF50 and the mutated forms of ORF50 are shown. ORF50 contains the basic domain, the leucine zipper motif (LZ), and the transcriptional activation domain (TAD). The LXXLL motif, which interacts with CBP, is located between amino acids 593 and 597 of ORF50. (B) The fold activation of the luciferase activity was determined with the p53-responsive reporters, and the following reporters were used: PG13-Luc (synthetic p53 binding site), MDM2-Luc (the promoter of MDM2 protein), and WWP-Luc (the promoter of p21). All of the ORF50 mutants were introduced into pME18S, a mammalian expression vector containing the SRα promoter and a Flag tag. 293T cells were transfected with the indicated vectors, and extracts were analyzed by blotting with anti-Flag antibody (upper right panel).