Chromatin Structure of the β-Globin Gene Family in Murine Erythroleukemia Cells

We have analyzed the chromatin structure of the β-major globin gene and other related β-globin genes in induced and uninduced murine erythroleukemia (MEL) cell nuclei. Nuclei were digested with either DNase I or micrococcal nuclease, and the purified DNA was hybridized to a set of cloned genomic DNA fragments covering the (3-globin gene region. This region consisted of two distinct domains as characterized by sensitivity to DNase I digestion. One domain was relatively sensitive and contained the potentially active or actively transcribed β-major and β-minor globin genes. The other, relatively insensitive domain contained the nontran-scribed embryonic and β-globin homologous genes. The sensitivity of these domains was not altered during erythroid differentiation. In nonerythroid cells, the entire globin gene family, including the adult and embryonic globin genes, was contained in a single relatively resistant domain. Micrococcal nuclease (MNase) also defined two general domains of nuclease sensitivity that coincided with those of DNase I. However, the relatively sensitive MNase domain containing the β-major and β-minor genes became more sensitive upon chemically stimulated erythroid differentiation. A detailed examination of the β-major globin gene revealed that the actual coding region became increasingly sensitive to micrococcal nuclease after differentiation while the 5′-flanking DNA did not. Thus, micrococcal nuclease was able to accurately define the primary transcription unit of the β-major gene.