Chromatin structure of the beta-globin gene family in murine erythroleukemia cells

We have analyzed the chromatin structure of the beta-major globin gene and other related beta-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 beta-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 beta-major and beta-minor globin genes. The other, relatively insensitive domain contained the nontranscribed embryonic and beta-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 beta-major and beta-minor genes became more sensitive upon chemically stimulated erythroid differentiation. A detailed examination of the beta-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 beta-major gene.