The mammalian BTG/Tob family gene products have anti-proliferative ability and are characterised by a conserved BTG domain. Tob subfamily members have the most extensive C-terminal regions. The BTG domain mediates interactions with the highly similar Caf1a (CNOT7) and Caf1b (CNOT8) catalytic subunits of the Ccr4-Not deadenylase complex. Overexpression of BTG/Tob proteins is associated with the inhibition of G1 to S-phase cell cycle progression and decreased cell proliferation in a variety of cell types.