High Quality Content by WIKIPEDIA articles! Tobacco etch virus (TEV) is a plant pathogenic virus of the family Potyviridae.TEV contains a highly site-specific protease, commonly called TEV protease. Biochemists have used this to their advantage, to create a protein purification system by incorporating TEV protease's recognition site into protein purification tags. A gene construct is created containing the protein of interest fused to a TEV protease recognition site, followed by an affinity tag, such as a Polyhistidine-tag. Following affinity chromatography, the purified protein is then treated with TEV protease. TEV protease cleaves at its recognition site, removing the affinity tag. This allows for affinity purification of proteins that are not well-behaved when fused to protein tags.