The winged-helix/forkhead protein myocyte nuclear factor β (MNF-β ) forms a co-repressor complex with mammalian Sin3B

Winged-helix}forkhead proteins regulate developmental events in both invertebrate and vertebrate organisms, but biochemical functions that establish a mechanism of action have been defined for only a few members of this extensive gene family. Here we demonstrate that MNF (myocyte nuclear factor)-β, a wingedhelix protein expressed selectively and transiently in myogenic precursor cells of the heart and skeletal muscles, collaborates with proteins of the mammalian Sin3 (mSin3) family to repress transcription. Mutated forms of MNF-β that fail to bind mSin3 are defective in transcriptional repression and in negative growth