Flap endonucleases (FENs, also known as 5' durgs in older references) are a class of nucleolytic enzymes that act as both

5'-3' Directionality, in molecular biology and biochemistry, is the end-to-end chemical orientation of a single strand of nucleic acid. In a single strand of DNA or RNA, the chemical convention of naming carbon atoms in the nucleotide pentose-sugar ...

exonucleases Exonucleases are enzymes that work by cleaving nucleotides one at a time from the end (exo) of a polynucleotide chain. A hydrolyzing reaction that breaks phosphodiester bonds at either the 3′ or the 5′ end occurs. Its close relative is th ...

and structure-specific

endonucleases Endonucleases are enzymes that cleave the phosphodiester bond within a polynucleotide chain. Some, such as deoxyribonuclease I, cut DNA relatively nonspecifically (without regard to sequence), while many, typically called restriction endonuclea ...

on specialised DNA structures that occur during the biological processes of

DNA replication In molecular biology, DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule. DNA replication occurs in all living organisms acting as the most essential part for biological inherita ...

DNA repair DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as radiation can cause DNA da ...

, and DNA recombination. Flap endonucleases have been identified in

eukaryotes Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bact ...

prokaryotes A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Conn ...

, archaea, and some

virus A virus is a wikt:submicroscopic, submicroscopic infectious agent that replicates only inside the living Cell (biology), cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and ...

es. Organisms can have more than one FEN homologue; this redundancy may give an indication of the importance of these enzymes. In prokaryotes, the FEN enzyme is found as an N-terminal domain of

DNA polymerase A DNA polymerase is a member of a family of enzymes that catalyze the synthesis of DNA molecules from nucleoside triphosphates, the molecular precursors of DNA. These enzymes are essential for DNA replication and usually work in groups to create ...

I, but some prokaryotes appear to encode a second homologue. The endonuclease activity of FENs was initially identified as acting on a DNA duplex which has a single-stranded 5' overhang on one of the strands (termed a "5' flap", hence the name flap endonuclease). FENs catalyse hydrolytic cleavage of the

phosphodiester bond In chemistry, a phosphodiester bond occurs when exactly two of the hydroxyl groups () in phosphoric acid react with hydroxyl groups on other molecules to form two ester bonds. The "bond" involves this linkage . Discussion of phosphodiesters is ...

at the junction of single- and double-stranded DNA. Some FENs can also act as 5'-3' exonucleases on the 5' terminus of the flap strand and on 'nicked' DNA

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (locomotion), the surface over which an organism lo ...

Protein structure Protein structure is the molecular geometry, three-dimensional arrangement of atoms in an amino acid-chain molecule. Proteins are polymers specifically polypeptides formed from sequences of amino acids, the monomers of the polymer. A single ami ...

models based on

X-ray crystallography X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angle ...

data suggest that FENs have a flexible arch created by two α-helices through which the single 5' strand of the 5' flap structure can thread. Flap endonucleases have been used in

biotechnology Biotechnology is the integration of natural sciences and engineering sciences in order to achieve the application of organisms, cells, parts thereof and molecular analogues for products and services. The term ''biotechnology'' was first used b ...

, for example the Taqman

PCR PCR or pcr may refer to: Science * Phosphocreatine, a phosphorylated creatine molecule * Principal component regression, a statistical technique Medicine * Polymerase chain reaction ** COVID-19 testing, often performed using the polymerase chain r ...

assay and the Invader Assay for mutation and single nucleotide polymorphism (SNP) detection.

References

External links

External lin
Flap endonucleases, 5'-3' exonucleases & 5' nucleases
{{DNA replication Biotechnology EC 3.1

See also

References

External links