The outer loop is formed by peptide bonds between a carboxyl terminus of an amino acid to the subsequent amino terminus of the next residue. The inner loop is closed by a tryptathionine linkage between 6-hydroxy-tryptophan and cysteine. In addition, α-amanitin is decorated with modified amino acid side chains (2S,3R,4R)-4,5-dihydroxy-isoleucine, trans-4-hydroxy-proline, which gives its high affinity for RNA polymerase II and III.[6]