Mutations of the GATA- or C/EBP-binding sites diminish MBP promoter activity (A) and mutations of the GATA- or C/EBP-sites does not prevent synergy (B). Jurkat cells were cotransfected with pXP2-MBP containing wild-type GATA-1 and C/EBP-sites, pXP2-MBP containing a mutated GATA-binding site, and/or pXP2-MBP containing a mutated C/EBP-binding site, along with 2 μg of pEF-GATA-1 and/or pEF-C/EBPβ expression vectors. The error bar represents the SEM for 3 independent experiments. Luciferase activity was normalized to β-galactosidase activity from a cotransfected CMV-βGal plasmid.