A protein that cleaves a DNA sequence at a specific point. There are 3 different kinds of Restriction Enzyme, with the most commonly used in molecular biology being Type II. This type of restriction enzyme cleaves pallandromic DNA sequences in double stranded DNA. For example, the enzyme EcoRI cleaves the following sequence:
to give two sticky ends
5'-G         AATTC-3'
3'-CTTAA         G-5'
Their function in nature is to protect bacteria from foreign DNA by chopping it into small fragments, which generally are not harmful. Bacteria prevent chopping their own DNA by methylation of self strands. Also known as: Restriction Endonucleases

See Also: DNA Fingerprinting