由該基因編碼的蛋白質屬于smad，一個類似于果蠅基因‘母親抗十五癱’（mad）和秀麗隱桿線蟲基因sma的基因產物的蛋白質家族。smad蛋白是介導多種信號通路的信號轉導和轉錄調節因子。這種蛋白介導轉化生長因子（tgf）-β的信號，從而調節多種細胞過程，如細胞增殖、凋亡和分化。該蛋白通過與受體激活的SMAD錨定蛋白（SARA）的相互作用被招募到TGFβ受體。作為對tgf-β信號的反應，該蛋白被tgf-β受體磷酸化。磷酸化誘導該蛋白與sara的分離，并與smad4家族成員相關聯。與Smad4的結合對于該蛋白向細胞核的轉運非常重要，在細胞核中它與靶啟動子結合并與其他輔助因子形成轉錄抑制復合物。該蛋白也可以被激活素1型受體激酶磷酸化，并介導激活素的信號。另外，已經觀察到該基因的剪接轉錄變體。[由RefSeq提供，2012年5月]
The protein encoded by this gene belongs to the SMAD, a family of proteins similar to the gene products of the Drosophila gene 'mothers against decapentaplegic' (Mad) and the C. elegans gene Sma. SMAD proteins are signal transducers and transcriptional modulators that mediate multiple signaling pathways. This protein mediates the signal of the transforming growth factor (TGF)-beta, and thus regulates multiple cellular processes, such as cell proliferation, apoptosis, and differentiation. This protein is recruited to the TGF-beta receptors through its interaction with the SMAD anchor for receptor activation (SARA) protein. In response to TGF-beta signal, this protein is phosphorylated by the TGF-beta receptors. The phosphorylation induces the dissociation of this protein with SARA and the association with the family member SMAD4. The association with SMAD4 is important for the translocation of this protein into the nucleus, where it binds to target promoters and forms a transcription repressor complex with other cofactors. This protein can also be phosphorylated by activin type 1 receptor kinase, and mediates the signal from the activin. Alternatively spliced transcript variants have been observed for this gene. [provided by RefSeq, May 2012]