SMAD9 is a 55-60kD R-Group member of the dwarfin/SMAD family of proteins. It is expressed by BMP-responsive cells, and serves to transmit information from the BMP receptor (BMPR) to the nucleus. In particular, following BMPR activation, SMAD9 is phosphorylated by the BMPR on its C-terminus, promoting heterodimerization with SMAD4 and its translocation into the nucleus. Here, SMAD9 binds to DNA and participates in gene activation. Human SMAD9 is 467aa in length. It contains a DNA-binding domain termed MH1 aa16-140 plus a receptor/transcription factor binding domain termed MH2 aa273-467. The C-terminus contains two phosphorylation sites at aa465 and aa467. There is one splice form that shows a deletion of aa224-260. Over aa158-223, human and mouse SMAD9 share 82% identy in aa sequence.