This gene encodes a SMAD protein, which mediates signaling in the TGF-beta pathway and regulates processes like cell proliferation, apoptosis, and differentiation. It interacts with the SMAD anchor for receptor activation (SARA) protein and is phosphorylated by TGF-beta receptors. Phosphorylation leads to dissociation from SARA and association with SMAD4, facilitating its nuclear translocation. In the nucleus, it forms a repressor complex with cofactors to regulate gene expression. This protein can also be phosphorylated by the activin type 1 receptor kinase to mediate activin signaling. Alternative splicing produces multiple transcript variants.