Acetylation of GATA-1 Is Required for Chromatin Occupancy.

All three hematopoietic GATA transcription factors GATA-1, GATA-2, and GATA-3 are acetylated, although the in vivo role of this modification remains unclear. It has been proposed that acetylation of GATA-1 increases its affinity for DNA in vitro, although this finding has not been observed by others. To study the role of GATA-1 acetylation, we examined the functions of an acetylation-defective mutant of GATA-1 in maturing erythroid cells. We found that removal of the acetylation sites in GATA-1 largely abrogates its biological activity but does not impair its nuclear localization, steady state protein levels, or its ability to bind naked GATA elements in vitro. However, chromatin immunoprecipitation (ChIP) experiments revealed that mutant GATA-1 was dramatically impaired in binding to its cellular target sites in vivo, including genes that are normally activated (α- and β-globin, EKLF, FOG-1, Band3, and AHSP) and repressed (GATA-2 and c-kit) by GATA-1. Together, these results suggest that acetylation is required for GATA-1 chromatin occupancy. These findings point to a novel function for transcription factor acetylation, perhaps by facilitating protein interactions required for stable association with chromatin templates in vivo. To identify proteins that interact with acetylated GATA-1, we performed peptide affinity chromatography using acetylated GATA-1 peptides. Using this technique coupled with mass spectrometry, several proteins that bind to GATA-1 peptides in an acetylation-dependent manner were identified. The identified proteins contain known acetyl-lysine binding modules (bromodomains) consistent with their binding properties. The in vivo role of these proteins with regard to GATA-1 function is being examined and will be discussed.