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NHEJ is a DNA repair mechanism which, unlike homologous recombination, does not require a long homologous sequence to guide repair. Whether homologous recombination or NHEJ is used to repair double-strand breaks is largely determined by the phase of cell cycle. Homologous recombination repairs DNA before the cell enters mitosis (M phase).
The most common form of HDR is homologous recombination. The HDR mechanism can only be used by the cell when there is a homologous piece of DNA present in the nucleus, mostly in G2 and S phase of the cell cycle. Other examples of homology-directed repair include single-strand annealing and breakage-induced replication.
In meiosis, non-sister homologous chromosomes pair with each other so that recombination characteristically occurs between non-sister homologues. In both meiotic and mitotic cells, recombination between homologous chromosomes is a common mechanism used in DNA repair .
In human cells, there are two main DSB repair mechanisms: Homologous recombination (HR) and non-homologous end joining (NHEJ). HR relies on undamaged template DNA as reference to repair the DSB, resulting in the restoration of the original sequence. [2] NHEJ modifies and ligates the damaged ends regardless of homology. [2]
While gene targeting relies on the Homology Directed Repair (HDR) (also called Homologous Recombination, HR) DNA repair pathway, targeted-mutagenesis uses Non-Homologous-End-Joining (NHEJ) of broken DNA. NHEJ is an error-prone DNA repair pathway, meaning that when it repairs the broken DNA it can insert or delete DNA bases, creating insertions ...
Homologous recombination is the exchange of genes between two DNA strands that include extensive regions of base sequences that are identical to one another. In eukaryotic species, bacteria, and some viruses, homologous recombination happens spontaneously and is a useful tool in genetic engineering.
Some DNA viruses encode a recombinase that facilitates homologous recombination. A well-studied example is the UvsX recombinase encoded by bacteriophage T4. [10] UvsX is homologous to bacterial RecA. UvsX, like RecA, can facilitate the assimilation of linear single-stranded DNA into an homologous DNA duplex to produce a D-loop.
In humans, RAD51 is a 339-amino acid protein that plays a major role in homologous recombination of DNA during double strand break repair.In this repair process, an ATP-dependent DNA strand exchange takes place in which a template strand invades base-paired strands of homologous DNA molecules.