Restriction enzyme digestion is a technique used to cut DNA at specific, predetermined sites. Restriction enzymes—also called restriction endonucleases—are molecular scissors that recognize short, palindromic DNA sequences and cleave the DNA at or near these sites.
How Restriction Enzyme Digestion Works
- Choosing the Enzyme
Each restriction enzyme recognizes a specific DNA sequence, typically 4–8 base pairs long. Common examples include EcoRI (GAATTC) and HindIII (AAGCTT). Scientists choose enzymes based on where they cut relative to the DNA region of interest.
- Setting Up the Reaction
The purified DNA is mixed with the restriction enzyme, a buffer specific to that enzyme, and water. The buffer provides the optimal salt concentration and pH for the enzyme to function. The mixture is incubated at the enzyme’s optimal temperature, usually 37°C.
- Incubation
During incubation, the enzyme scans the DNA for its recognition sequence. Upon finding a match, it cuts the DNA backbone at precise locations. If the DNA contains multiple recognition sites, it will be cut into multiple fragments of varying sizes.
- Heat Inactivation
After sufficient incubation time, the reaction is often heated to 65–80°C to denature and inactivate the enzyme, stopping the digestion. The resulting DNA fragments can then be analyzed by agarose gel electrophoresis or used in downstream applications like cloning.
