The sequence APRTPGGRR contains a native sequence derived from bovine myelin basic protein amino acids 95-98 (PRTP). The rest of the sequence is not derived from a native sequence, but is a synthetic construct. This substrate is specific for MAP kinases: p44MAPK [extracellular signal-regulated kinase 1 (ERK1)] and p42MAPK (ERK2). It contains the consensus sequence Pro-X-(Ser/Thr)-Pro that is recognized by MAP kinase. This peptide is the most efficient substrate for phosphorylation reaction by ERK. The substrate is phosphorylated by kinases on threonine 97 and can also be phosphorylated by MAPK p38.