GST (Glutathione S-Transferase) is a 26kDa protein encoded by the parasitic helminth Schistosoma japonicum and widely used in the pGEX family of GST plasmid expression vectors as a fusion protein with foreign proteins. It can provide both an easily detectable Tag and a simple purification process with little effect on the biological function of the protein of interest. Numerous vectors containing GST-Tag have been developed for both prokaryotic and eukaryotic systems.