The locus control region (LCR) far upstream of the human beta-like globin genes is defined by the preferential chromatin accessibility/DNase I hypersensitivity of four constituent DNA sites HS4, 3, 2, and 1. In an attempt to understand the mechanism of LCR function during early stages of erythropoiesis, a new polymerase chain reaction (PCR) method has been developed to examine the chromatin structure/DNase I hypersensitivity of the LCR in progenitor cells logistically available in limited cell numbers. In erythroid progenitors as well as in multipotent cells with erythroid potential, hypersensitive sites HS4, 3, 2, and 1 were present and the chromatin structure of the LCR was accessible. Moreover, the chromatin structure of the LCR underwent dynamic changes during erythropoiesis. In early erythroid progenitors, the HS2 site was more accessible than the HS3 site. In more mature erythroid progenitors, HS2 became less accessible than HS3 and the other sites. The results indicate that the transcriptional program of the globin genes is encoded, at least in part, in the chromatin accessibility of the LCR. This globin program was apparently initiated in multipotent cells and maintained in erythroid progenitors. Furthermore, the program could be modulated in response to cellular changes accompanying differentiation of the progenitor cells.

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