In an earlier paper we identified a tissue-specific enhancer in the 3' flanking region of the chicken adult beta-globin gene. In this paper we analyze the properties of this enhancer. Deletion analysis and transient expression assays show that the domain responsible for activation of transcription is at most 136 base pairs long. Specific factors that bind to discrete sequences within the enhancer DNA are found in extracts of embryonic and adult erythrocytes and in brain. These factors are specific for the tissue or the erythrocyte developmental stage and protect at least five discrete regions in or near the enhancer against DNase I digestion in "footprinting" experiments. Four of these regions reside wholly within the 136-base-pair functional enhancer domain, which also comprises a site in chromatin that is hypersensitive to nucleases. The nature of the binding sites and the program of appearance of the factors during development suggest that a subset of these interactions may be responsible for the developmental specificity of the enhancer.

Emerson, B. M., Nickol, J. M., Jackson, P. D., & Felsenfeld, G. (1987). Analysis of the tissue-specific enhancer at the 3’ end of the chicken adult beta-globin gene. Proceedings of the National Academy of Sciences, 84(14), 4786–4790.