Another solution that is often quickest is to make fusions between genes Use a carrier sequence a sequence which is known to be expressed well in E. coli . Contains the necessary signals for good expression. TAGS Carrier sequences can also function as a TAG enabling easy purification of the protein using affinity chromatography. The expressed protein purified from lysed cells under non-denaturing conditions by adsorption with glutathione agarose beads. Often does not compromise the antigenicity or functional activity of the foreign polypeptide.
Proteins often remain soluble.
Disadvantages Protease cleavage depends upon accessibility of protease recognition site. A second purification step is needed to remove the cleaved GST from mixture. Since it relies on enzymes substrate recognition the protein must be in its native form to bind to glutathione. Uses many of the protein modification, processing and transport systems present in higher eukaryotic cells. Viral genome is large and can accommodate large segments of DNA Baculoviruses are noninfectious to vertebrates and their promoters are inactive in mammalian cells.