GATA-1 inhibits PU.1 expression. (A) PU.1/Sfpi1 mRNA expression by real-time reverse-transcribed polymerase chain reaction (RT-PCR) after GATA-1 rescue in G1ME cells relative to untransduced cells. Bars represent the mean of 3 independent experiments ± SD. (B) PU.1 protein expression by Western blotting of sorted GFP⁺ G1ME cells before and after GATA-1 restoration. PU.1 expression in untransduced G1ME cells approximates endogenous murine erythroleukemia (MEL) cells. Two bands are visualized for PU.1, most likely due to posttranslational modifications. HDAC2 indicates histone deacetylase 2. (C) PU.1/Sfpi1 mRNA expression by RT-PCR in G1ME cells relative to the myeloid cell line 416B. Bars represent the mean of 3 independent experiments ± SD.