Smad oligomerisation. Smad oligomerisation. Pictorial representation of the plasma membrane receptor kinases that phosphorylate the C-termini of R-Smads (light colour), leading to homo-oligomerisation (a dimer shown for simplicity). Hetero-oligomerisation of R-Smads with the Co-Smad (dark colour) is shown leading to dimers and trimers (see text). The MH1 and MH2 domains are drawn and coloured according to the depiction of Table 1. Small black circles represent the di-phosphate modification of the SXS motif and small, double-headed arrows point to the protein interface between phosphorylated C-termini and the MH2 domain. For references see Chacko et al. (Chacko et al., 2001) and Shi (Shi, 2001). Aristidis Moustakas et al. J Cell Sci 2001;114:4359-4369 © The Company of Biologists Limited 2001