Restriction endonuclease -

Restriction endonucleases are enzymes, found in bacteria, that cut DNA; they are called molecular scissors.
Each restriction endonuclease recognises a specific base sequence in the DNA, usually a palindromic sequence of 4 to 8 base pairs, called its recognition sequence.
It binds to the DNA and cuts each of the two strands at specific points within this sequence, in their sugar-phosphate backbones.
For example, EcoRI recognises 5'-GAATTC-3' and cuts between G and A on both strands, producing sticky ends.
Because the cuts are made only at specific sites, the same enzyme always gives the same fragments, which is what makes recombinant DNA technology possible.
It does not cut randomly, and it neither synthesises DNA nor restricts DNA synthesis in the nucleus.
So a restriction endonuclease cuts the DNA molecule at specific sites.