DNase I hypersensitive sites of globin genes of uninduced Friend erythroleukemia cells and changes during induction with dimethyl sulfoxide.

We compared the DNase I sensitivity of beta-globin genes in dimethyl sulfoxide-treated and untreated Friend erythroleukemia cells to determine whether the induced globin synthesis in these cells is associated with any change in the chromatin conformation of the globin genes. The beta-globin genes were preferentially sensitive to DNase I digestion in both uninduced and induced cells as compared to the alpha-fetoprotein gene and bulk DNA. Additionally, we detected specific cleavage sites in the region of the beta-major globin gene when nuclei from uninduced cells were digested with DNase I. Following induction, a 2- to 4-fold increase in DNase I digestion at one of these hypersensitive sites was observed while digestion at the other sites was greatly reduced. We have localized this primary hypersensitive site to the 5' end of the beta-major gene. To determine when during induction these observed changes in chromatin structure occur, nuclei were digested with DNase I after 6 to 120 h of induction with dimethyl sulfoxide. Some change in chromatin conformation was detectable by 12 h of induction and the configuration characteristic of the fully induced state was established by 24 h of induction. Since it has been reported that increases in beta-globin mRNA levels are not detected until 18-20 h of induction, it appears that alterations in the chromatin conformation of the globin genes may precede the changes in other biochemical parameters associated with differentiation and may be an early reflection of commitment to the erythroid pathway.