Other Pages Restriction Enzymes Restriction endonucleases are protein enzymes that recognize specific nucleotide sequences and cleave both strands of the DNA containing those sequences.
Recognition sequences for many enzymes are the same on both strands.
Such recognition sequences are said to be palindromic . Commonly used restriction enzymes always cleave the DNA strands at a fixed position relative to the recognition sequence. Positions of cleavage relative to the recognition sequence depend on the enzyme. Products with flush ends or 5' or 3' overhanging single-stranded ends may be produced. Because the sites of cleavage of long DNA molecules are determined by their nucleotide sequence, the long DNAs are broken into discrete sized fragments.