Restriction Enzyme (Restriction Endonuclease)


A restriction enzyme (also called a restriction endonuclease) is a type of protein that can cut DNA molecules at specific sequences of nucleotides. These sequences are called restriction sites and they are usually four to eight base pairs long and palindromic, meaning they read the same on both strands of the DNA.

Restriction enzymes are produced by bacteria as a defense mechanism against foreign DNA, such as from viruses or other bacteria. By cutting the foreign DNA into smaller fragments, the bacteria can prevent it from replicating or expressing harmful genes. The bacteria protect their own DNA from being cut by the same restriction enzymes by adding methyl groups to their restriction sites, making them unrecognizable by the enzymes.

Restriction enzymes are widely used in molecular biology and biotechnology as tools for manipulating DNA. They can be used to cut DNA into smaller pieces for analysis, to insert or remove genes from DNA molecules, to create recombinant DNA by joining fragments from different sources, and to generate DNA libraries for sequencing or cloning. Restriction enzymes are also essential for some techniques such as polymerase chain reaction (PCR), gel electrophoresis, Southern blotting, and DNA fingerprinting.