Figure 1

A schematic structure of the Smads. The N-terminal MH1 domain (light blue) and C-terminal MH2 domain (dark blue) are conserved among Smads. The non-conserved regions including the linker are shown in white. The two Serine (S) residues at the C-terminus of R-Smads that are phosphorylated by the type I receptor are marked with asterisks. MH Mad homology domain; PY, the proline-tyrosine (PPXY) motif identified by the E3 ligases Smurf1 and Smurf2; SAD, Smad4 activation domain.