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

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Abstract
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 consisted 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.