Exonuclease III is an enzyme

Enzyme

Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

 that belongs to the exonuclease

Exonuclease

Exonucleases are enzymes that work by cleaving nucleotides one at a time from the end of a polynucleotide chain. A hydrolyzing reaction that breaks phosphodiester bonds at either the 3’ or the 5’ end occurs. Its close relative is the endonuclease, which cleaves phosphodiester bonds in the middle ...

 family. ExoIII catalyzes the stepwise removal of mononucleotides from 3´-hydroxyl termini of duplex 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...

. A limited number of nucleotides are removed during each binding event, resulting in coordinated progressive deletions within the population of DNA molecule

Molecule

A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...

s.

Function

The preferred substrates are blunt or recessed 3´-termini, although ExoIII also acts at nicks in duplex DNA to produce single-strand gaps. The enzyme is not active on single-stranded DNA, and thus 3´-protruding termini are resistant to cleavage. The degree of resistance depends on the length of the extension, with extensions 4 bases or longer being essentially resistant to cleavage. This property is used to produce unidirectional deletion

Deletion

Deletion is the act of deleting or removal by striking out material, such as a word or passage, that has been removed from a body of written or printed matter.Deletion may refer to:*File deletion, a way of removing a file from a computer's file system...

s from a linear molecule with one resistant (3´-overhang) and one susceptible (blunt or 5´-overhang) terminus.

ExoIII activity depends partially on the DNA helical structure and displays sequence dependence (C>A=T>G).

ExoIII has also been reported to have RNase H, 3´-phosphatase and AP-endonuclease activities.

Regulation

Temperature

Temperature

Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

, salt

Salt

In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...

 concentration

Concentration

In chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. Four types can be distinguished: mass concentration, molar concentration, number concentration, and volume concentration...

 and the ratio of enzyme to DNA greatly affect enzyme activity, requiring reaction

Chemical reaction

A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...

conditions to be tailored to specific applications.