Characterization of Gly cophorin A Transcripts: Control by the Common Erythroid-Specific Promoter and Alternative Usage of Different Polyadenylation Signals1

Abstract

Glycophorins A (GPA) and B (GPB) are specifically expressed in human erythrocytes and express MN and Ss blood group antigens. While the GPB gene produces one transcript, the GPA gene produces three or four transcripts of different sizes. To understand the mechanisms of production of the different transcripts and erythroid-specific expression, we characterized the transcripts and the transcriptional regulatory regions of the glycophorin A gene. The transcriptional start site was determined by primer extension and S1 nuclease protection analysis, and it was found that all of the transcripts start at one major site. The nucleotide sequence of the newly isolated longest GPA cDNA revealed several polyadenylation signal sequences. To determine which polyadenylation signals are utilized, cDNA clones encoding GPA were isolated from a cDNA library of human erythroleukemia cell line K562 and the 3'-regions of the cDNAs were specifically amplified by the polymerase chain reaction. These results showed that five different polyadenylation signals of the GPA gene are utilized and the size and abundance of the transcripts are consistent with those detected by Northern blot analysis of K562 mRNAs. The 5'-flanking sequence was found to contain several binding motifs for the transcription factors, which were also found in other erythroid-specific genes. These motifs include the binding sites for the GATA-1 and NF-E2 erythroid-specific transcription factors, in addition to Sp1 transcription factor. The 5'-sequence from -750 to +36 relative to the transcriptional start site could confer only a low basal transcriptional activity in K562 cells and Friend erythroleukemia cells. This activity was significantly increased after Friend erythroleukemia cells were differentiated by dimethylsulfoxide. These results suggest that the 5' region regulates the glycophorin gene expression in erythroid-specific fashion.