SfiI is a restriction enzyme that can cleave two DNA sites simultaneously to leave 3-base 3' overhangs. It acts as a homo-tetramer and recognises a specific eight base-paid palindromic DNA sequence. After binding two copies of its recognition sequence, SfiI becomes activated leading to cleavage of all four DNA strands. The structure of SfiI consists of a central twisted beta-sheet surrounded by alpha-helices.

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