Tenascin-C (TNC) binds syndecan-3 (Salmivirta et al. 1991, Koyama et al. 1996) Syndecans are type I transmembrane proteins, with an N-terminal ectodomain that contains several consensus sequences for glycosaminoglycan attachment and a short C-terminal cytoplasmic domain. Syndecan-1 and -3 glycosaminoglycan attachment sites occur in two distinct clusters, one near the N-terminus and the other near the membrane-attachment site, separated by a proline and threonine-rich 'spacer'. Syndecan ectodomain sequences are poorly conserved in the family and between species, but the transmembrane and cytoplasmic domains are highly conserved. Syndecan-1 and -3 form a subfamily. Syndecan-3 on the cell surface is frequently oligomeric (Asundi & Carey 1995). Syndecans bind extracellular ligands via their attached heparan sulphate chains, playing roles in cell to matrix and cell to cell adhesion.