The minimal promoter plays a major role in silencing of the galago gamma-globin gene in adult erythropoiesis.

The human gamma-globin gene and its orthologous galago gamma-globin gene evolved from an ancestral epsilon-globin gene. In galago, expression of the gamma-gene remained restricted to the embryonic stage of development, whereas in humans, expression of the gamma-gene was recruited to the fetal stage. To localize the cis-elements responsible for this developmentally distinct regulation, we studied the expression patterns of the human gamma-gene driven by either the human or the galago gamma-promoters in transgenic mice. gamma-gene transcription driven by either promoter reached similar levels in embryonic erythropoiesis. In adult erythropoiesis the gamma-gene was silenced when controlled by the galago gamma-promoter, but it was expressed at a high level when it was linked to the human gamma-promoter. By a series of gamma-promoter truncations the sequences required for the down-regulation of the galago gamma-globin gene were localized to the minimal promoter. Furthermore, by interchanging the TATA, CCAAT, and CACCC elements between the human and galago minimal promoters we found that whereas each box made a developmentally distinctive contribution to gamma-globin gene expression, the CACCC box was largely responsible for the down-regulation of the gamma-gene in adult erythropoiesis.