Speaker: Marjorie Brand The Use of Quantitative Proteomics to Study Erythroid Differentiation Differentiation of erythroid cells from stem cell progenitors is a complex process involving combinatorial interactions between transcription factors and cofactors, ultimately regulating gene expression and chromatin structure. To better understand the process governing erythroid differentiation and ?-globin transcription, we are mapping interactions between transcription factors and cofactors that are important for this process. Using the isotopically labeled reagents (ICAT and iTRAQ) we compare protein-protein interactions quantitatively at different stages of differentiation. Here, I will describe our latest findings on the changes in the interaction partners of the hematopoietic transcription factor NF-E2/p45 during erythroid differentiation. I will also present our follow up studies on particular NF-E2/p45-interacting complexes implicated in methylation of histone H3. These studies permitted us to identify and delineate the role of two competing methyltransferases in regulating chromatin structure on the ?-globin locus during erythroid differentiation.