Endonuclease
In molecular biology, endonucleases are enzymes that cleave the phosphodiester bond within a polynucleotide chain (namely DNA or RNA).
Endonucleases differ from exonucleases, which cleave the ends of recognition sequences instead of the middle (endo) portion.
Most restriction endonucleases cleave the DNA strand unevenly, leaving complementary single-stranded ends.
These enzymes are often used in genetic engineering to make recombinant DNA for introduction into bacterial, plant, or animal cells, as well as in synthetic biology.
Type I can cleave at random sites of about 1000 base pairs or more from the recognition sequence and it requires ATP as source of energy.
Some examples of type II restriction endonucleases include BamHI, EcoRI, EcoRV, HindIII, and HaeIII.
Type III, however, cleaves the DNA at about 25 base pairs from the recognition sequence and also requires ATP in the process.
In mouse embryonic stem cells, an intermediate stage of crosslink repair involves production of double-strand breaks.
[12] MUS81/EME1 is a structure specific endonuclease involved in converting interstrand crosslinks to double-strand breaks in a DNA replication-dependent manner.
The phage T4 denV gene encodes endonuclease V that catalyzes the initial steps in the repair of these UV-induced thymine dimers.
[citation needed] During apoptosis, Apoptotic endonuclease DFF40 is activated to initiate controlled cellular disassembly.
The precise role of endonucleases in this context is to cleave the DNA at specific sites, generating fragments with defined lengths.
This process is integral to the seamless synthesis and joining of Okazaki fragments, contributing to the overall continuity of the newly replicated DNA strand.
[15][16] Endonucleases, more specifically endoribonuclease, play a crucial role in RNA processing, a fundamental step in gene expression.
[18] DICER and DROSHA also from the RNase III family play a role in the processing pre-miRNA to functional miRNA.
Pontocerebellar hypoplasias (PCH) represent a group of neurodegenerative autosomal recessive disorders that is caused by mutations in three of the four different subunits of the tRNA-splicing endonuclease complex.
