Analysis of GAL4-CREB fusions by cotransfection assay. (A) Schematic structure of GAL4-CREB fusion constructs and reporter gene construct. (B) HEL cells were cotransfected with the pG4-CAT reporter gene and a gene encoding GAL4(_1-147), GAL4-CREB▵LZ, or GAL4-CREB▵LZM1 and then treated with medium alone (negative control), TPO (100 ng/mL), Epo (2 U/mL), hemin (10⁻⁷ mol/L), forskolin (10⁻⁵ mol/L), or PMA (10⁻⁷ mol/L) for 30 minutes. CAT promoter activity was measured as folds of activations with respect to HEL cells left untreated (medium alone). Data are reported as the means ± SD of three independent transfection experiments performed in duplicate.