GATA-1 is the founding member of the GATA family of transcription factors. GATA-1 and GATA family member GATA-2 are expressed in erythroid and megakaryocytic lineages, in which they play a crucial role in cell maturation and differentiation. GATA-1 regulates the transcription of many specific and nonspecific erythroid genes by binding to DNA at the consensus sequence WGATAR, which is recognized by all of the GATA family of transcription factors. However, it was identified in eosinophilic cells and also in Sertoli cells in testis. Its activity depends on close cooperation with a functional network of cofactors, among them Friend of GATA, PU.1, and CBP/p300. The GATA-1 protein structure has been well described and includes two zinc fingers that are directly involved in the interaction with DNA and other proteins in vivo. GATA-1 mutations in the zinc fingers can cause deregulation of required interactions and lead to severe dysfunction in the hematopoietic system.