Nuclear proteins that interact with the beta maj globin promoter start to accumulate in MEL cells within 12 hours of induction and RNA copies of the promoter successfully compete their binding in vitro.

The induction of differentiation in mouse erythroleukemia (MEL) cells by dimethylsulfoxide (DMSO) is characterized by increased transcription of globin genes. We have determined that DMSO treated cells increase the levels of nuclear factors capable of overall interactions with the beta maj globin promoter during the initial 24 h post induction, as measured by gel mobility analysis. Two unprocessed beta maj globin mRNA precursors, which are present in MEL cell nuclei early in differentiation, were previously shown to contain the 5' promoter flanking region, and thereby provided the nucleus with a pool of regulatory sequences in multiple RNA copies. We have studied the effect of RNA copies of the promoter region on binding interactions between DNA sequences of the beta maj globin promoter and nuclear factors that interact with these sequences. The promoter region RNA transcripts competed effectively for DNA binding proteins in vitro, while the antisense RNA from the same region did not. The most pronounced competition was observed with proteins from 12 h after DMSO induction, when the concentration of the DNA binding proteins was still increasing. Since the 'upstream' transcripts predominate at 12 h after DMSO induction, these results indicate that the promoter region transcripts may influence the equilibrium of binding between the beta maj globin promoter and the nuclear factors that bind to this region during DMSO induction.