The transcription factor GATA-1 is essential for the development of the erythroid and megakaryocytic lineages. GATA-1 regulates the expression of all erythroid-restricted genes examined to date, including globins. Mutations in the GATA-1 gene occur in patients with anemias, thrombocytopenias, and leukemias. Here, we focus on the mechanism by which GATA-1 regulates gene is expression. Previous work funded under this grant showed that GATA-1 associates with the acetylase CBP in vivo and in vitro and that GATA-1 is acetylated by CBP at conserved, functionally important sites. Restoration of GATA-1 activity in the GATA-1-deficient cell line G1E leads to localized increases in CBP recruitment and concomitant histone acetylation at the beta-globin locus in vivo, indicating that GATA-1 acts in part by regulating chromatin structure. Specific Aim #1: Given the importance of site-specific modifications of histones, we will determine the exact sites within histones that are acetylated (or otherwise modified) in response to GATA-1 activation in vivo. This will serve in part to understand which chromatin modifiers are recruited by GATA-1 and form the basis for studies examining the molecular consequences of targeted histone modification. Specific Aim #2: The essential GATA-1 cofactor FOG-1 is required for histone modifications at certain GATA-1-dependent regulatory regions. This Aim addresses the role of FOG-1 during GATA-1-induced chromatin remodeling. Specific Aim #3: Preliminary results using microarrays suggest that GATA-1 represses nearly as many genes as it activates. Repression of some of these, which includes the cell cycle regulator c-myc, requires cooperation between GATA-1 and FOG-1. Little is known about the repressive functions of GATA-1. This Aim examines the roles of GATA-1 and FOG-1 during transcriptional repression at the c-myc locus. An important aspect of this work will be the regulation of chromatin structure that accompanies gene repression and the conditions that determine whether GATA- 1 will activate or repress gene expression. An important long-term goal of these studies is to identify chromatin remodeling enzymes that are recruited to GATA-1-dependent genes. These might serve as novel drug targets for intervention in hemoglobinopathies and other blood diseases, similar to compounds such as histone deacetylase inhibitors, which are currently in clinical trials [unreadable] [unreadable]