Phylogenetic tree of serine-kinase groups. Phylogenetic tree of serine-kinase groups whose targets can be found in the protein structure database (PDB) according to the original Hanks and Hunter classification scheme  and associated sequence logos . Kinases with high similarity tend to share similar targets. The major classes of kinase targets are characterized by a proline and glutamate next to the central serine, CMGC group I, II, II and respectively ATM, a group with preferentially negatively charged amino acid residues, CMGC IV and AGC IV, and a large group of targets with an arginine and lysine at the second or third position relative to the central serine, CaMK-Group and AGC-Group except the AGC IV sub family. For kinase families PKA, PKC, as well as CKII and MAPK most targets with resolved structure were available and were used for kinase family-specific predictors in this study.