The Ets family of transcription factors are DNA-binding proteins implicated in lymphoid development and activity. This family includes Ets-1, Ets-2, Erg-1-3, Elk-1, ETV-1, Elf-1, NERF, PU.1, PEA3, ERM, FEV, ER8l, Fli-1, TEL, Spi-B, ESE-1, ESE-3A and Net. They are characterized as monomeric transcription factors that bind the DNA site GGA(A/T) through a unique winged helix-turn-helix motif known as the Ets domain. The ability of Ets transcription factors to bind DNA and activate transcription is regulated through phosphorylation. PU.1 transcription factors, including Spi-1, Spi-B and Spi-C, are closely related Ets family members that share a conserved divergent sequence within the Ets domain, which enables them to bind to AGAA sites.