E. coli bacteria are a common host for the expression of recombinant proteins used in a wide range of applications. Plasmids are circular DNA constructs which may encode instructions for the synthesis of an engineered protein by the desired host cells. Following transformation and selection of bacterial colonies containing the plasmid, the recombinant protein is expressed and purified. Poly-histidine tagging and Nickel ion chromatography are commonly used to isolate large quantities of highly-purified target proteins. This video will demonstrate the procedures involved, including expression of a His-tagged recombinant protein in bacteria, purification of the protein using Nickel ion affinity chromatography, and analysis using SDS-PAGE. Protein expression and purification is presented by James Wright and directed by Rosemary Clyne.