This gene encodes a SMAD protein, part of a family involved in signal transduction and transcriptional regulation. It mediates the TGF-beta signaling pathway, regulating processes like cell proliferation, apoptosis, and differentiation. The protein is recruited to TGF-beta receptors via interaction with the SMAD anchor for receptor activation (SARA). Phosphorylation by TGF-beta receptors causes dissociation from SARA and association with SMAD4, enabling nuclear translocation. In the nucleus, the protein binds to target promoters and forms a transcription repressor complex. It can also be phosphorylated by activin receptor kinase, mediating activin signaling. Alternative splice variants of this gene have been observed.