RNase protection and sequence alignment of the proximal promoter region of the human and mouse βc chain genes. (A) RNase protection was used to determine transcription start sites. Specific protected fragments of 44, 45, 50, and 58 nucleotides were observed in βc expressing HL-60, butyric acid (BA)-treated HL-60, U937, TF-1, and THP-1 cell lines, but not in the HeLa and tRNA control lanes. The integrity of these start sites was confirmed by 5′ RACE analysis on HL-60–derived polyA⁺ RNA. (B) The putative TFIID/TBP binding sites are indicated in boldface and underlined, the first exons are indicated in bold face, and transcription start sites, identified by RNase protection and 5′ RACE, are indicated by asterisks. Several putative binding sites for different transcription factor families, including cEts, cMyb, MZF-1, GATA-1, STAT, cMyc, and C/EBP are identified in the human sequence. Ets-binding sites studied in this report are named −65 and −45 and are indicated in boldface. Furthermore, these elements are conserved in the murine sequence.