Exonuclease

Exonucleases are enzymes that work by cleaving nucleotides one at a time from the end (exo) of a polynucleotide chain.

Its close relative is the endonuclease, which cleaves phosphodiester bonds in the middle (endo) of a polynucleotide chain.

[1][2] In both archaea and eukaryotes, one of the main routes of RNA degradation is performed by the multi-protein exosome complex, which consists largely of 3′ to 5′ exoribonucleases.

Since that time, there have been numerous discoveries including: exonuclease, II, III, IV, V, VI, VII, and VIII.

In Escherichia coli the dnaQ gene encodes the ε subunit of DNA polymerase III .

It acts as a 3’→5’ DNA directed proofreading exonuclease that removes incorrectly incorporated bases during replication.

The Rat1 works just like the human type (Xrn2) and Xrn1 function in the cytoplasm is in the 5' to 3' direction to degrade RNAs (pre-5.8s and 25s rRNAs) in the absence of Rat1.

[17][18] In beta Coronaviruses, including SARS-CoV-2, a proof reading exonuclease, nsp14-ExoN, that is part of the viral genome is responsible for recombination that is implicated in novel strain emergence.