Space-filling drawing of an engineered TAL effector/nuclease bound to double-helical DNA. TALE proteins contain a series of alpha-helical hairpin domains, each of which binds an individual DNA base, so that the protein recognizes a long, very specific DNA sequence. This engineered construct attaches the specific FOK1 nuclease to one end of the TALE protein, and when two copies bind as a dimer the nuclease cleaves both strands of the DNA. Drawn by David Goodsell from PDB files 1FOK (nuclease/DNA) and 3UGM (TALE/DNA).