Enhancer dependent expression of the chicken beta-hatching globin gene during erythroid differentiation.

The activity of the chicken beta H globin gene promoter has been analysed in functional assays in both chicken and murine erythroleukaemia cells. Sequences between -251 and -146 bp, in the presence or absence of the chicken beta globin locus enhancer, strongly repress transcription in erythroid cells before and after the induction of terminal differentiation. A 50 bp sequence (-98 to -146 bp), which contains adjacent cGATA-1 and NF1 protein binding sites in vitro, and which is bound by non-histone protein in vivo, is essential for full promoter activity. Mutagenesis studies indicate that both protein binding sites are required. During terminal differentiation, both the absence of repressor and the presence of the erythroid enhancer are required for maximal promoter activity, suggesting that the beta A, beta epsilon and beta H globin gene promoters compete for the enhancer during development.