Abstract
We identify and describe the properties of an enhancer within the chicken α-globin gene cluster. This cluster consists of one gene (π) expressed only in primitive erythrocytes and two (α
A
and α
D
) expressed in both primitive and definitive cell lineages. The genes are linked together in the order 5′-π-α
D
-α
A
-3′ and occupy a region about 10 kilobase pairs long. The enhancer is located at the 3′ end of the cluster, about 750 base pairs 3′ to the α
A
translation stop site. When assayed by transfection into either primitive or definitive primary chicken erythrocytes, this element stimulated expression from plasmids containing the α
D
- or α
A
-globulin gene promoters. Except for sites in the α-globin promoters, no other stimulatory activity was observed in DNA taken from other regions of the α-globin locus. Moderate resolution DNase I hypersensitivity studies as well as DNase I footprinting revealed three regions of protein binding, each containing a similar core DNA sequence within the enhancer element. Gel mobility shift studies demonstrated that all three regions bind the recently identified erythrocyte-specific factor, EryfI, which has binding sites in the regulatory regions of all chicken globin genes. Our data suggest that the enhancer we have identified may act in vivo only on the α
A
gene; expression of the α
D
gene is affected by another EryfI site located in the α
D
promoter. Such a mechanism would be consistent with the observed relative abundances of α
A
- and α
D
-globin in vivo. The simplicity of these regulatory elements may reflect the limited repertoire of expression of these genes during development.