Multiple origins of transcription in the 4.5 Kb upstream of the epsilon-globin gene.

By a combination of primer extension and S1 mapping, we have identified and characterized at least nine epsilon-globin initiation sites in the 4.5 kb upstream of the canonical mRNA cap site. These occur in four regions, -65 to -250, -900, -1480, and -4500 bp from the translation initiation codon ATG. Transcripts from eight sites yield sufficient material for direct RNA analysis and in all of these instances the molecules are capped. Approximately 10%-15% of epsilon-globin transcripts originate from these upstream sites in both an erythroleukemic cell line and purified erythroblasts from first-trimester human embryos. In three established cell lines derived from adult non-erythroid tissue, low levels of transcription of the epsilon-globin gene occur, but the RNA molecules originate exclusively from one of the upstream sites identified in erythroid cells. These findings suggest modification of the current models of transcription of globin genes.