A protein complex that consists of only SMAD proteins; may be homomeric or heteromeric. Heteromeric complexes act as transcription factors while homomeric complexes exist but are transcriptionally inactive. Hetero- versus homotrimerization is largely enthalpy driven. [GOC:bhm, GOC:mah, PMID:9670020]
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Collection
C5: Ontology GO: Gene Ontology GO:CC: GO Cellular Component