One method of artificially creating these proteins is known as oligomerized pool engineering or OPEN. A phage display selection procedure can be used to engineer nucleases based on this structure, which have applications in gene targeting. A version 
One method of artificially creating these proteins is known as oligomerized pool engineering or OPEN. A phage display selection procedure can be used to engineer nucleases based on this structure, which have applications in gene targeting. A version of this domain containing a beta-hairpin at the C-terminus is the Treble clef, while Air2p and the HIV nucleocapsid protein contain a version known as the gag knuckle. Steroid hormone receptors contain one of these structures, which also occur in Egr1 and was originally discovered in the Xenopus protein TFIIIA. The classical version it contains two cysteine and two histidine residues near its recognition helices, which coordinate to a namesake metal ion. For 10 points, name this DNA-binding protein domain which contains a series of alpha helices that "grab" DNA.
One method of artificially creating these proteins is known as oligomerized pool engineering or OPEN.
{Zinc finger} (accept "zinc finger {nucleases}" until mentioned)