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HaeIII is one of many restriction enzymes (endonucleases) discovered since 1970. It was the third endonuclease to be isolated from the Haemophilus aegyptius bacteria, and has a molecular weight of 37126. The enzyme's recognition site—the place where it cuts DNA molecules—is the GGCC nucleotide sequence. This enzyme's gene has been sequenced and cloned.

Mechanism of action[edit]

The enzyme cleaves the DNA at the positions where the GGCC sequence is found. The cleavage occurs between the second and the third nucleotides (G and C). The resulting DNA fragments are known as restriction fragments. HaeIII cuts both strands of DNA in the same location, yielding restriction fragments with blunt ends. Heat denaturation occurs at 80°C after 20 minutes [1]