HaeIII is one of the 100+ restriction enzyme

Restriction enzyme

A Restriction Enzyme is an enzyme that cuts double-stranded DNA at specific recognition nucleotide sequences known as restriction sites. Such enzymes, found in bacteria and archaea, are thought to have evolved to provide a defense mechanism against invading viruses...

s (endonuclease

Endonuclease

Endonucleases are enzymes that cleave the phosphodiester bond within a polynucleotide chain, in contrast to exonucleases, which cleave phosphodiester bonds at the end of a polynucleotide chain. Typically, a restriction site will be a palindromic sequence four to six nucleotides long. Most...

s) discovered since 1970. It was isolated from the Haemophilus aegyptius

Haemophilus influenzae biogroup aegyptius

Haemophilus influenzae biogroup aegyptius is a causative agent of acute and often purulent conjunctivitis, more commonly known as pink eye...

bacteria

Bacteria

Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

, and has a molecular weight of 37126. The enzyme's recognition site—the place where it cuts DNA

DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

 molecules—is the GGCC nucleotide

Nucleotide

Nucleotides are molecules that, when joined together, make up the structural units of RNA and DNA. In addition, nucleotides participate in cellular signaling , and are incorporated into important cofactors of enzymatic reactions...

 sequence. This enzyme's gene

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

 has been sequenced and cloned.

Mechanism of action

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

Guanine

Guanine is one of the four main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine . In DNA, guanine is paired with cytosine. With the formula C5H5N5O, guanine is a derivative of purine, consisting of a fused pyrimidine-imidazole ring system with...

 and C

Cytosine

Cytosine is one of the four main bases found in DNA and RNA, along with adenine, guanine, and thymine . It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached . The nucleoside of cytosine is cytidine...

). The resulting DNA fragments are known as restriction fragment

Restriction fragment

A restriction fragment is a DNA fragment resulting from the cutting of a DNA strand by a restriction enzyme , a process called restriction. Each restriction enzyme is highly specific, recognising a particular short DNA sequence, or restriction site, and cutting both DNA strands at specific points...

s. 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