Induction and reversible regulation of E2AER DNA binding activity. (A) Detection of E2AER protein. Whole cell lysates were collected from E2A+/+, E2A-/-, E2AER/+, E2AER/ER, and E2AGFP/GFP Abelson-transformed preB cell lines and analyzed by Western Blot for E2A protein expression using an anti-E2A antibody. E2A+/+, E2AER/+, and E2AER/ER Abelson cells were also cultured with tamoxifen prior to analysis, as indicated. E2A+/+, E2AGFP/GFP, and E2A-/- lines were used as positive and negative controls for E2A proteins. ERK2 was used as a loading control. (B and C) Analysis of E2AER DNA binding activity. E2AER/ER Abelson-transformed preB cells were cultured (B) without and with tamoxifen for 1, 6 and 10 hr and (C) with tamoxifen and upon tamoxifen withdrawal for 1 and 6 hr. Nuclear extracts were analyzed by gel shift for E2A DNA-binding using a μE5 probe. Anti-E2A antibody was used to demonstrate specificity (Ab). E2A-DNA complexes (arrow) and antibody-shifted complexes (arrow head) are indicated. *Non-specific band.