SMAD2 and SMAD3 do not bind DNA efficiently. They must interact with DNA-binding proteins to activate transcription. FOXH1 interacts with phospho-SMAD2 and phospho-SMAD3 complexed with CO-SMAD (SMAD4) at promoters containing the Activin Response Element (Zhou et al. 1998, Yanagisawa et al. 2000, inferred from Xenopus in Chen et al. 1996, Chen et al. 1997, Yeo et al. 1999). Follicle-stimulating hormone beta subunit (FSHB) and the Lim1 homeobox gene (LXH1) are examples of genes regulated by Activin.