ABSTRACT
Restriction enzymes recognize specific nucleotide sequences in double-stranded deoxyribonucleic acid (DNA), that are usually four, five or six nucleotides long, and then cut both strands of the DNA at specific locations. When a DNA molecule is cut by a restriction enzyme, the DNA fragments from that restriction digest can be separated by gel electrophoresis. The DNA digest separates into a series of bands representing the restriction fragments. Restriction enzymes are isolated from bacteria, where they play a role in protecting the host cell against virus infection. Restriction maps are important experimentally during recombinant DNA work, both to plan where individual DNA molecules should best be cut and to monitor the progress of the experiment. Some polymorphisms affect the size of fragments generated by a particular restriction enzyme by changing a nucleotide in the recognition sequence and so eliminating a cut site.
