GATA1 (Globin transcription factor 1) is a Cys2/Cys2 zinc finger DNA binding protein that is expressed primarily in erythroid, megakaryocytic, mast cells and eosinophilic cells. It belongs to the GATA family of transcription factors. GATA1 is a transcriptional activator which probably serves as a general switch factor for erythroid development. It binds to DNA sites with the consensus sequence [AT]GATA[AG] within regulatory regions of globin genes and of other genes expressed in erythroid cells. The protein also plays an important role in erythroid development by regulating the switch of fetal hemoglobin to adult hemoglobin. Mutations in this gene have been associated with X-linked dyserythropoietic anemia and thrombocytopenia. Acquired somatic mutations in GATA1 occur in virtually all children with Down's Syndrome, congenital transient myeloproliferative syndrome (TMD) and acute megakaryocytic leukemia.