Relative activity of wild-type and mutGATA γ-globin promoter plus enhancer plasmids in uninduced K562 and MEL cells. Activities are calculated relative to the wild-type γ-globin promoter-luciferase plasmid without enhancer. The activity values are presented as the mean ± SEM and n denotes the number of assays performed. The wild-type γ-globin promoter data in part A are repeated from Figs 2 and 3.