THE ERYTHROID PROTEIN CGATA-1 FUNCTIONS WITH A STAGE-SPECIFIC FACTOR TO ACTIVATE TRANSCRIPTION OF CHROMATIN-ASSEMBLED BETA-GLOBIN GENES

The chick beta-globin gene is regulated developmentally within erythroid cells by the interaction of multiple proteins with the promoter and the 3' enhancer. These interactions are correlated with changes in chromatin structure, which are characteristic of the actively expressed gene. Using in vitro chromatin assembly and transcription with staged erythroid extracts, we have determined the critical proteins required to activate expression of nucleosome-reconstituted beta-globin genes. These genes contain a specialized TATA box at -30 (GATA) through which the erythroid-restricted protein cGATA-1 and TFIID both function to regulate different steps in beta-globin expression. We find that TBP (TATA-binding protein) alone can activate transcription of beta-globin chromatin templates from promoters mutated to a canonical TATA box but is ineffective on those containing the normal -30 GATA site. The occupancy of this site by cGATA-1 also fails to generate efficient expression of beta-globin chromatin unless combined with a stage-specific protein, NF-E4, that binds to an adjacent site. However, NF-E4 does not function with TBP to derepress nucleosome-assembled beta-globin genes. We propose that the developmental regulation of beta-globin expression is achieved, in part, by the requirement of an erythroid protein and a stage-specific factor, rather than TBP, to activate chromatin through a specialized TATA box.