Where Found

• In nature, restriction enzymes are found in bacteria and archaebacteria. They have been found in over 230 species of bacteria.
  
  

Purpose

• Bacteria and archaebacteria use restriction enzymes to cut up any foreign DNA they encounter that comes into the cell. Foreign DNA typically comes from viruses or bacteriophages that attempt to invade bacteria and archaebacteria.
  
  

Evolution

• Restriction enzymes are believed to have originally evolved to help protect the microorganisms from invasion by viruses, and later by bacteriophages. Scientists think these enzymes were designed to cut viral DNA into pieces, rendering it harmless.
  
  

Individualized

• Different species of microorganisms make different restriction enzymes, depending on the types of foreign DNA that commonly invade their cells.
  
  

Self-Preservation

• Inside bacteria and archaebacteria, the DNA of the organisms themselves is modified to prevent the restriction enzymes from cutting their own DNA into pieces. This limits restriction enzyme activity to foreign DNA only.