Principle: Restriction endonuclease can specifically bind to a specific site in or near a DNA sequence called restriction endonuclease recognition sequence to cut double-stranded DNA.

Enzymatic digestion can be single enzyme digestion or double enzyme digestion. The operation of single enzyme digestion is relatively simple, but if the two enzymes use different buffer components (mainly different salt ion concentrations) or different reaction temperatures, the following measures can be taken: 1) First, perform enzyme digestion, then precipitate with ethanol to recover DNA molecules, and then perform another enzyme digestion; 2) firstly, enzyme digestion with low salt demand is carried out, then salt ion concentration is added to the enzyme reaction demand with high salt, and a second enzyme is added for enzyme digestion; 3) Double enzyme digestion with common buffer. Specifically, it should be carried out according to the reaction requirements of the enzyme to avoid the loss of activity as much as possible.