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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). It occurs during and shortly after DNA replication, in the S and G 2 phases of the cell cycle, when sister chromatids are more easily ...
It repairs breaks that occur on only one of DNA's two strands, known as single-strand gaps. The RecF pathway can also repair double-strand breaks in DNA when the RecBCD pathway, another pathway of homologous recombination in bacteria, is inactivated by mutations. [1] Like the RecBCD pathway, the RecF pathway requires RecA for strand invasion.
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]
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.
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.
Figure 2 RecBCD pathway of homologous recombination where ATP is in excess. Both the RecD and RecB subunits are helicases, i.e., energy-dependent molecular motors that unwind DNA (or RNA in the case of other proteins). The RecB subunit in addition has a nuclease function. [5]
Here, homologous recombination (HR) can, in principle, provide specificity to the integration process, but for eukaryotes it is compromised by an extremely low efficiency. Although meganucleases, zinc-finger- and transcription activator-like effector nucleases (ZFNs and TALENs) are actual tools supporting HR, it was the availability of site ...
A high-frequency recombination cell (Hfr cell) (also called an Hfr strain) is a bacterium with a conjugative plasmid (for example, the F-factor) integrated into its chromosomal DNA. The integration of the plasmid into the cell's chromosome is through homologous recombination .