A NOVEL DEVELOPMENTAL REGULATORY MOTIF REQUIRED FOR STAGE-SPECIFIC ACTIVATION OF THE EPSILON-GLOBIN GENE AND NUCLEAR FACTOR-BINDING IN EMBRYONIC ERYTHROID-CELLS

Members of the human beta-globin gene family are expressed at discrete stages of development and therefore provide an important model system for examining mechanisms of temporal gene regulation. We have previou sly shown that expression of the embryonic beta-like globin gene (epsi lon) is mediated by a complex array of positive and negative upstream control elements. Correct developmental stage- and tissue-specific gen e expression is conferred by synergistic interactions between a positi ve regulatory element (termed epsilon-PRE II) which is active only in embryonic erythroid cells and at least two other regulatory domains up stream of the epsilon-globin gene promoter. A nuclear factor highly en riched in cultured embryonic erythroid cells and in mouse embryonic yo lk sac binds to a novel, evolutionarily conserved sequence within epsi lon-PRE II. We show here that binding of this factor to the conserved element within epsilon-PRE II is critical for transcriptional activity . Point mutations that interfere with protein binding to epsilon-PRE I I abolish transcriptional activation of the constitutive epsilon-globi n promoter. Adult erythroid nuclei (from cultured cells or adult mouse liver) also contain a factor that binds to this region, but the compl ex formed migrates more rapidly during nondenaturing electrophoresis, suggesting either that distinct proteins bind to epsilon-PRE II or tha t a single protein is differentially modified in these cells in a way that modulates its activity. Several lines of evidence suggest that th e binding factors in embryonic and adult erythroid cells are distingui shed by posttranscriptional differences.