Transcription regulator that plays an central role in red blood cell differentiation. Essential cofactor that acts via the formation of a heterodimer with transcription factors of the GATA family GATA1 and GATA2. Such heterodimer can both activate or repress transcriptional activity, depending on the cell and promoter context. Acts as a repressor of red blood cells, probably by modulating activity of GATA1. Interacts with corepressor CTBP. Interacts with the N-terminal zinc-finger of GATA1 and probably GATA2. Predominantly expressed in heart and brain. Also expressed in ventral blood island and adult spleen. Some of the CCHC FOG-type zinc fingers probably directly bind to GATA-type zinc fingers. The Tyr residue adjacent to the last Cys of the CCHC FOG-type zinc finger is probably essential for the interaction with GATA-type zinc fingers (By similarity). Belongs to the FOG (Friend of GATA) family.