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TEV proteases are the 27kDa catalytic domains of the NIa (Nuclear Inclusion a) protein encoded by Tobacco Etch Virus (TEV), where TEV proteases cut polyproteins into single proteins during biogenesis. TEV proteases recognize a linear epitope of the general form E-Xaa-Xaa-Y-Xaa-Q-(G/S) and cut the linkage between Q and G/S (Xaa can be freely substituted because variability in these positions was found in the natural cleavage sites of TEV’s polyprotein). Comparison of cleavage efficiency of different substract sequences demonstrated that “ENLYFQS” is the most efficient substrate sequence. The high-specificity of TEV’s cleavage makes it a popular tool for direct expression in living cells and protein purification.