A GST-tag is often used to separate and purify proteins that contain the GST-fusion protein. The tag is 220 amino acids (roughly 26 kDa) in size,[40] which, compared to tags such as the Myc-tag or the FLAG-tag, is quite large. It can be fused to either the N-terminus or C-terminus of a protein. In addition to functioning as a purification tag, GST acts as a chaperone for the attached protein, promoting its correct folding, as well as preventing it from becoming aggregated in inclusion bodies when expressed in bacteria. The GST tag can easily be removed following purification by addition of thrombin protease if a suitable cleavage site has been inserted between the GST-tag and the protein of interest (which is usually included in many commercially available sources of GST-tagged plasmids).