Previous deletion mutations study has suggested that the GNE kinase domain is responsible for dimerization, while a segment of residues between the epimerase and kinase domains, residues 360-382, is a potential site for trimerization [18] . Our gel filtration data ( Figure 3) show that the kinase domain exists predominantly as a dimer in the solution, with small amounts of monomer and a higher order oligomer. The apparent molecular weight of the oligomer fits a hexamer of the kinase domain (see also below). However, the possibility of a tetramer [19] cannot be completely ruled out due to the low resolution of the gel-filtration column at this molecular size The GNE kinase domain was crystallized in space group P3 1 21 with three molecules in the asymmetric unit. Protein interface and assembly analysis using the PISA server [20] suggests that two of the three molecules dimerize through the C-lobe with an average buried surface area of 1587 Å 2 per molecule ( Figure 4 ) whereas the third molecule dimerizes with a two-fold symmetry related molecule through the same C-lobe ( Figure 5a ). The solvation free energy gain upon formation of the interface, D i G, is 224.2 kcal?mol 21 , indicating that the dimer interface is very stable and may not simply be a crystal packing artifact.