A protein complex composed of a single type of SMAD family proteins. In the absence of Smad4, phosphorylation of R-SMADs results in their homotrimerization. However, these complexes do not appear to import into the nucleus and are assumed to be transcriptionally inactive.
Synonyms:
narrow_synonym:
SMAD1 homotrimer complex; SMAD1 protein complex; SMAD2 homotrimer complex; SMAD2 protein complex; SMAD3 homotrimer complex; SMAD3 protein complex