(i) They cut DNA duplex at specific points.
They are molecular scissors.
Rules : Restriction endonucleases are named by using first letter of the name of genus followed by first two letters of species from which these enzymes are isólated. All the three letters are written in italics.
(ii) Each restriction endonuclease recognises a specific palindromic base sequence in foreign DNA and cuts sugar phosphate backbone of both strands of double helix at specific points. These ends are called as sticky ends. The sticky ends of 2 different molecules of DNA cut by same restriction endonuclease arc thenjoined by ligase to form a recombinant DNA.