The Glutathione S-transferase (GST) gene fusion system supplied by GE Healthcare is used for the cloning, expression, purification and detection of fusion proteins. pGEX plasmids are designed for inducible, high-level expression of genes or gene fragments as fusions with GST from Schistosoma japonicum. Fusion proteins are easily purified from bacterial lysates by affinity chromatography utilizing GSTs binding affinity for Glutathione. The GST Western Blotting Detection kit facilitates the detection of GST fusion proteins on Western blots using chemiluminescence. This method may be used for crude bacterial sonicates, column eluates or purified GST fusion proteins. Unlike biochemical assays, this method is not dependent on the functional activity of GST, which can be affected by folding of the fusion protein.