GATA-binding factor 1 or GATA-1 (also termed Erythroid transcription factor) is the founding member of the GATA family of transcription factors. This protein is widely expressed throughout vertebrate species. In humans and mice, it is encoded by the GATA1 and Gata1 genes, respectively. These genes are located on the X chromosome in both species.

GATA1 regulates the expression (i.e. formation of the genes' products) of an ensemble of genes that mediate the development of red blood cells and platelets. Its critical roles in red blood cell formation include promoting the maturation of precursor cells, e.g. erythroblasts, to red blood cells and stimulating these cells to erect their cytoskeleton and biosynthesize their oxygen-carrying components viz., hemoglobin and heme. GATA1 plays a similarly critical role in the maturation of blood platelets from megakaryoblasts, promegakaryocytes, and megakaryocytes; the latter cells then shed membrane-enclosed fragments of their cytoplasm, i.e. platelets, into the blood.

In consequence of the vital role that GATA1 has in the proper maturation of red blood cells and platelets, inactivating mutations in the GATA1 gene (i.e. mutations that result in the production of no, reduced levels of, or a less active GATA1) cause X chromosome-linked anemic and/or bleeding diseases due to the reduced formation and functionality of red blood cells and/or platelets, respectively, or, under certain circumstances, the pathological proliferation of megakaryoblasts. These diseases include transient myeloproliferative disorder occurring in Down syndrome, acute megakaryoblastic leukemia occurring in Down syndrome, Diamond–Blackfan anemia, and various combined anemia-thrombocytopenia syndromes including a gray platelet syndrome-type disorder.

Reduced levels of GATA1 due to reductions in the translation of GATA1 mRNA into its transcription factor product are associated with promoting the progression of myelofibrosis, i.e. a malignant disease that involves the replacement of bone marrow cells by fibrous tissue and extramedullary hematopoiesis, i.e. the extension of blood cell-forming cells to sites outside of the bone marrow.