HaeIII is one of many restriction enzymes (endonucleases) a type of prokaryotic DNA that protects organisms from unknown, foreign DNA. It is a restriction enzyme used in molecular biology laboratories. It was the third endonuclease to be isolated from the Haemophilus aegyptius bacteria. The enzyme's recognition site—the place where it cuts DNA molecules—is the GGCC nucleotide sequence which means it cleaves DNA at the site 5′-GG/CC-3. The recognition site is usually around 4-8 bps. This enzyme's gene has been sequenced and cloned. This is done to make DNA fragments in blunt ends. HaeIII is not effective for single stranded DNA cleavage.