The N-terminal effector-binding domain of the Restriction Endonuclease EcoRII has a DNA recognition fold, allowing for binding to 5'-CCWGG sequences. It assumes a structure composed of an eight-stranded beta-sheet with the strands in the order of b2, b5, b4, b3, b7, b6, b1 and b8. They are mostly antiparallel to each other except that b3 is parallel to b7. Alternatively, it may also be viewed as consisting of two mini beta-sheets of four antiparallel beta-strands, sheet I from beta-strands b2, b5, b4, b3 and sheet II from strands b7, b6, b1, b8, folded into an open mixed beta-barrel with a novel topology. Sheet I has a simple Greek key motif while sheet II does not [1].

1: Crystal structure of type IIE restriction endonuclease EcoRII reveals an autoinhibition mechanism by a novel effector-binding fold. Zhou XE, Wang Y, Reuter M, Mucke M, Kruger DH, Meehan EJ, Chen L; J Mol Biol. 2004;335:307-319. PMID:14659759