Structures of the active sites of SET-domain protein methyltransferases. Hydrogen bonds are rendered as dashed lines and residue numbers are indicated in the single-letter amino-acid code. (a-c) The carbon atoms of substrates and products are illustrated in purple to distinguish them from protein residues (gray). (a) The cofactor-binding site of SET7/9 with bound AdoMet (PDB code 1N6A.pdb). (b) The lysine-binding pocket of SET7/9 in complex with methylated K4 (MeK4) of histone H3 from the crystal structure of the ternary complex SET7/9:AdoHcy:histone H3 MeK4 peptide (1O9S.pdb). (c) The lysine-binding channel of DIM-5 bound to K9 of histone H3 from the structure of the ternary complex DIM-5:AdoHcy:histone H3 peptide (1PEG.pdb). (d,e) Protein-substrate-binding clefts of SET-domain protein methyltransferases. The binding sites are rendered as transparent molecular surfaces. For clarity, the carbon atoms of histone H3 are depicted in cyan and the enzymes in green. (d) The protein-substrate-binding site of SET7/9 in complex with a histone H3 peptide from the structure of the ternary complex (1O9S.pdb). The white area is the methyltransfer pore. (e) Substrate-binding cleft of DIM-5 bound to a histone H3 peptide from the ternary complex structure (1PEG.pdb).