Induced transcription of the mouse beta-globin transcription unit in erythroleukemia cells. Time-course of induction and of changes in chromatin structure.

The transcription of the beta-globin genes in mouse erythroleukemia cells has been examined by hybridizing labeled RNA obtained from isolated nuclei after chain elongation in the presence of [alpha-32P]UTP. There is induction of at least 30-fold of beta maj globin transcription after cells are treated with either dimethylsulfoxide or hexamethylene bisacetamide. The induction requires 36 to 48 hours to be maximal, during which time the cells double about three to four times. During this time, a site in the beta maj DNA region becomes hypersensitive to DNase. The development of this hypersensitive site is co-ordinate with the transcriptional increase. The induced transcripts in the beta-globin region are alpha-amanitin-sensitive (and therefore are RNA polymerase II products). An examination of weak transcriptional signals to DNA fragments upstream of the beta maj globin gene in uninduced mouse erythroleukemia cells and in cells that do not make globin is also reported. The low level of hybridization to the upstream regions in uninduced erythroleukemia cells, in L cells (a fibroblast) and in a strain of erythroleukemia cells that no longer make globin are not equally sensitive to alpha-amanitin as in the induced signal. These experiments help define the inducible transcription unit for beta maj globin mRNA production.