Although mammalian galectins lack con ventional signal sequences, they reach the cell surface by a novel mechanism a nd bind to glycoconjugates in on the plasma membrane and in the extracellular matrix (Barondes et al., 1994 ). The galectins consist of globular galectin-type CRDs with relatively mi nor accessory domains ( Cooper and Barondes, 1999) . A galectin-type CRD comprises a/b sandwich si milar in overall topology to the L-type CRDs. However, the lack of sequence si milarity and the different way in which sugar-binding sites are constructed in these two families of domains suggest that this topological similarity result s from convergent evolution. Most galectins contain multiple sugar-binding sit es, due to the presence of two galectin-type CRDs in a single polypeptide or a s a result of dimerisation. A common function of the galectins may be to cross link N-acetyllactosamine-containing structures found at cell surfaces and in t he extracellular matrix. Comparison of all the galectin sequences reveals conservation primarily of inw ardly facing hydrophobic residues in b strands in the b-sandwich of the galect in fold ( Lobsanov et al., 1993; Liao et al., 1994; Leonidas et al., 1998). Eight residues that form the galactoside-binding s ite are conserved in most mammalian galectins, although a vertebrate galectin containing only six of the canonical galactose-binding residues interacts with mannose rather than galactose ( Swaminathan et al., 1999). Galectin-3 (also known as MAC-2 antigen; CBP-35 or IgE-binding protein), a 35 Kd lectin which binds immunoglobulin E and which is composed of two domai ns: a N-terminal domain that consist of tandem repeats of a glycine/proline- rich sequence and a C-terminal galaptin domain. Galectin-3 has been shown to m odulate apoptosis by interactions with bcl family members.