SILENCING OF ^A-GLOBIN GENE EXPRESSION DURING ADULT DEFINITIVE ERYTHROPOIESIS MEDIATED BY GATA-1-FOG-1-Mi2 COMPLEX BINDING AT THE -566 GATA SITE

Departments of Biochemistry and Molecular Biology, and Anatomy and Cell Biology, University of Kansas Medical Center, Kansas City, KS 66160

^* To whom correspondence should be addressed. Email: kpeterson{at}kumc.edu.

	Abstract

Autonomous silencing of -globin transcription is an important developmental regulatory mechanism controlling globin gene switching. An adult stage-specific silencer of the ^A-globin gene was identified between -730 to -378 relative to the mRNA start site. A marked copy of the ^A-globin gene inserted between LCR 5'HS1 and the -globin gene was transcriptionally silenced in adult -YAC transgenic mice, but deletion of the 352 bp region restored expression. This fragment reduced reporter gene expression in K562 cells and GATA-1 was shown to bind within this sequence at the -566 GATA site. Further, Mi2 protein, a component of the NuRD complex, was observed in erythroid cells with low -globin levels, whereas only a weak signal was detected when -globin was expressed. Chromatin immunoprecipitation of fetal liver tissue from -YAC transgenic mice demonstrated that GATA-1, FOG-1 and Mi2 were recruited to the ^A-globin -566 or the ^G-globin -567 GATA sites when -globin expression was low (day 18), but not when -globin was expressed (day 12). These data suggest that during definitive erythropoiesis, -globin gene expression is silenced, in part, by binding a protein complex containing GATA-1, FOG-1, and Mi2 at the -566/-567 GATA sites of the proximal -globin promoters.