Identification of an alternate delta-globin mRNA in adult human erythroid cells

Here we describe the identification and characterization of an alternate delta-globin mRNA (Alt-d) discovered during high-throughput sequencing of mRNA from adult human erythroid cells. Alt-d mRNA shares the same coding region, splicing pattern, downstream untranslated region, and site of polyadenylation with the previously defined delta-globin (Delta) mRNA. Alt-d mRNA encodes an additional 145 nt in the upstream untranslated region, suggesting an alternative site of transcriptional initiation and transcription through the previously defined promoter, which contains several protein-binding motifs and a TATA box. Northern blot and PCR analyses demonstrated a restricted expression of Alt-d in fetal liver, bone marrow, and adult reticulocytes. Quantitative PCR demonstrated an Alt-d expression pattern similar to that of the Delta transcripts. In addition to intergenic RNA species and the dominant delta-globin transcripts, these data suggest that a third form of RNA is produced from low-level transcription through the delta-globin gene promoter.