Bidirectional control of the chicken beta- and epsilon-globin genes by a shared enhancer

An enhancer specific to erythroid cells was identified previously in the 3' flanking sequence of the chicken adult beta-globin gene and shown to act on the beta-globin promoter. This enhancer lies between the adult beta-globin gene and the embryonic epsilon-globin gene, about equidistant from the two promoters. To determine whether this enhancer acts also on the epsilon-globin promoter, we constructed plasmids containing the enhancer and either the beta- or the epsilon-globin promoter fused to the bacterial chloramphenicol acetyltransferase gene. Primary chicken erythrocytes of both primitive and definitive lineages were transfected with these plasmids. We show that the enhancer is able to stimulate expression from the epsilon-globin promoter as well as the beta-globin promoter. Levels of expression change with the developmental stage of the cell in a way that is partially consistent with the observed developmental regulation of the beta- and epsilon-globin genes in vivo. There appear to be no other enhancer elements either 5' of the epsilon-globin gene or within 6 kilobase pairs of its 3' end. Thus, the enhancer between the beta- and epsilon-globin genes apparently serves to regulate both genes.