exonucléase

Exonucléase, commonly referred to in English as exonuclease, designates a class of nucleases that catalyze the removal of nucleotides from the ends of polynucleotide chains. Unlike endonucleases, which cut within the chain, exonucleases release nucleoside monophosphates one by one as the reaction proceeds from an exposed terminus.

Exonucleases are classified by the direction in which they remove nucleotides: 5' to 3' exonucleases digest from the 5' end toward the 3' end, while 3' to 5' exonucleases digest from the 3' end toward the 5' end. They act on DNA, RNA, or both, and may prefer single-stranded or double-stranded substrates, depending on the enzyme. Many require divalent metal ions, such as magnesium or manganese, and employ a catalytic mechanism common to many nucleases.

Biological roles of exonucleases include DNA replication and repair, recombination, RNA maturation, and RNA quality control and decay. In cellular processes, these enzymes help generate correct termini for ligation, remove erroneous or damaged nucleotides, and participate in RNA processing pathways.

In biotechnology and molecular biology, exonucleases are tools for manipulating nucleic acids. They are used to trim DNA ends, remove excess primers or single-stranded overhangs, digest unwanted nucleic acids during cloning or sequencing workflows, and facilitate downstream applications that require defined termini or clean templates. In eukaryotes, exonuclease activity is a component of larger complexes such as the exosome, which provides 3' to 5' exoribonuclease activity for RNA processing and turnover.