The protein encoded by this gene is involved in the TGF-beta signaling pathway that results in an inhibition of the proliferation of hematopoietic progenitor cells. The encoded protein is activated by BMP type 1 receptor kinase. Three transcript variants encoding the same protein have been found for this gene. Transcriptional modulator activated by BMP (bone morphogenetic proteins) type 1 receptor kinase. SMAD5 is a receptor-regulated SMAD (R-SMAD). May form trimers with the co-SMAD SMAD4. Interacts with PEBP2-alpha subunit and SMURF1. Interacts with SUV39H1 and SUV39H2. Interacts (via MH2 domain) with LEMD3. Interacts with WWP1.