Exodeoxyribonucleases

Exodeoxyribonucleases, often shortened to exonucleases, are enzymes that degrade DNA from its ends. They catalyze the hydrolysis of phosphodiester bonds at either the 5' or 3' terminus of a DNA strand. This process releases mononucleotides, the individual building blocks of DNA. Exonucleases play crucial roles in various cellular processes, including DNA repair, replication, and recombination.

There are two main types of exonucleases based on their direction of action. 5' to 3' exonucleases remove nucleotides from the 5' end of a DNA strand, while 3' to 5' exonucleases remove them from the 3' end. Some enzymes can act in both directions. The specificity of exonucleases can also vary; some are specific for single-stranded DNA, while others can act on double-stranded DNA.

In DNA replication, certain exonucleases are involved in proofreading. For example, a 3' to 5' exonuclease activity is often coupled with a DNA polymerase's synthetic activity. If the polymerase incorporates an incorrect nucleotide, the exonuclease can remove it, allowing the polymerase to insert the correct one. Exonucleases are also essential in DNA repair pathways, where they help to remove damaged or mismatched DNA segments. During recombination, exonucleases can process DNA ends to facilitate the exchange of genetic material. Their precise roles and mechanisms are actively researched in molecular biology and genetics.