Transcriptional potential of the γ-globin gene is dependent on the CACCC box in a developmental stage-specific manner

To test the role of CACCC box on γ-globin gene activation, the CACCC box was deleted or mutated and γ-gene expression was monitored in transgenic mice. Disruption of the CACCC box had no effect on γ-gene expression in the cells of embryonic erythropoiesis but it strikingly reduced γ-gene expression in fetal erythropoiesis, and abolished γ-gene expression in adult erythroid cells. The CACCC mutation diminished HS formation, as well as TBP and polII recruitment at the γ-gene promoter; however, it only resulted in slight or no effects on histone H3 and H4 acetylation in adult erythropoiesis. Our findings indicate that each basic cis element of the proximal γ-gene promoter, i.e. CACCC, CCAAT or TATA box, can be disrupted without affecting the activation of γ gene in embryonic erythroid cells. We propose that the trans factors recruited by the three boxes interact with each other to form a ‘promoter complex’. In embryonic erythropoiesis the locus control region enhancer is able to interact with the complex even when components normally binding to one of the motifs are missing, but it can only activate an intact ‘promoter complex’ in adult erythroid cells.