A Valuable Chemical Scissors

In the 1970s researchers discovered enzymes in bacteria that attach to any DNA molecule when they find specific sequences of base pairs. They reliably slice the molecule between two of those pairs. For example, the restriction enzyme EcoR1 (obtained from Escherichia coli bacteria) attaches to DNA when it detects the sequence GAATTC and cuts between the G and the A.

Bacteria use these enzymes as a rudimentary immune system. The enzyme attacks and destroys the DNA of an invading virus. The bacterium protects itself from the action of the enzyme by making a slight alteration at the target sequence on its own DNA.

Researchers have identified several hundred restriction enzymes, allowing them to cut DNA molecules at many specific points. The tool has proved immensely useful in biochemical research.