An Hsp70 promoter drives expression of a hybrid zinc finger nuclease, which consists of a DNA-binding domain composed of zinc fingers linked to a nonspecific DNA-cleavage domain derived from the Poke\FokI restriction endonuclease. The zinc finger domains have been designed to recognise the target sequence 5'-GTAGTAGCT-3' which is within ry exon 3.
Zzzz\ZFNhs.ryA and Zzzz\ZFNhs.ryB are used in combination to induce double strand breaks within the endogenous ry gene sequence.