Residue interaction matrix. Residue interaction matrix R. Rows show the amino acids in the phosphosite regions and columns are amino acids in the catalytic domain of the kinases. Negatively charged amino acids (D, E) are red, positively charged amino acids (K, R, H) are blue, hydrophobic amino acids (F, I, L, V) green, proline as orange, and phosphorylation site residues (S, T, Y) are represented as gray. ‘x’ also corresponds to the absence of an amino acid, which occurs for phosphosites located at the N-and C-termini of proteins. This figure was derived from knowledge of the structure and charge of the amino acid side chains.