Physical association of p300 and the Gcn5/Trrap (GNAP) complex with ZBP-89 in human erythroid cells. (A) Tandem anti-FLAG, streptavidin affinity purification assay from uninduced K562 cells stably expressing FLAG and metabolically biotin tagged ZBP-89 (^FLAG-Bio ZBP89) versus control cells expressing birA alone. Western blot analysis of the final copurified proteins for the indicated proteins is shown. Streptavidin indicates streptavidin-horseradish peroxidase (SA-HRP) direct blot; IN′, 2% input; and IP, streptavidin affinity purified material. (B) Western blot analysis of indicated proteins during erythroid commitment and maturation from expanded CD34⁺ cells. Time represents days after the cells were switched into differentiation medium. (C) Quantitative ChIP assays for Gcn5 occupancy at key cis-regulatory regions within the β- and α-globin loci from cells on day 7 of differentiation. Fold enrichments are shown relative to an exonic region of the β-actin gene. Data represent the mean of 3 independent experiments ± SEM.