Transcription regulator that plays an essential role in erythroid and megakaryocytic cell differentiation. Essential cofactor that acts via the formation of a heterodimer with transcription factors of the GATA family GATA1, GATA2 and GATA3. Such heterodimer can both activate or repress transcriptional activity, depending on the cell and promoter context. The heterodimer formed with GATA proteins is essential to activate expression of genes such as NFE2, ITGA2B, alpha- and beta-globin, while it represses expression of KLF1. May be involved in regulation of some genes in gonads. May also be involved in cardiac development, in a non-redundant way with ZFPM2/FOG2. Interacts with the N-terminal zinc-finger of GATA1, GATA2 and GATA3. Interacts with corepressor CTBP2; this interaction is however not essential for corepressor activity in erythropoiesis. Interacts with TACC3. Mainly expressed in hematopoietic tissues. Expressed in the spleen, a primary site of hematopoiesis in the adult mouse, as well as in the liver and testis, but not in the heart, brain, lung, kidney, or skeletal muscle. Among hematopoietic cell lines, it is strongly expressed in erythroid and megakaryocytic cell lines. Expressed at low level in several lymphoid and early myeloid cell lines. Not expressed in mast cell and macrophage lines. Expressed in the heart, where it colocalizes with GATA4, GATA5 and GATA6. First expressed in two extraembryonic mesodermal derivatives, the yolk sac and the allantois in 8.5 dpc embryos. Localized to the embryonic red blood cells within the yolk sac blood islands. The CCHC FOG-type zinc fingers 1, 2, 3 and 5 bind directly to GATA-type zinc fingers. The Tyr residue adjacent to the last Cys of the CCHC FOG-type zinc finger is essential for the interaction with GATA-type zinc fingers. Belongs to the FOG (Friend of GATA) family.