Eschericia coli is a frequently used host, since it facilitates protein expression by its relative simplicity, its inexpensive and fast high density cultivation, the well known genetics and the large number of compatible molecular tools available. Affinity tags have been observed to improve protein yield, to prevent proteolysis and to increase solubility in vivo. The purification of his-tagged proteins is based on the use of a chelated metal ion as an affinity ligand. Enterokinases are generally used for digestion of fusion proteins as they cleave target on the C terminal side of the...