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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.
The RuvABC is a complex of three proteins that resolve the Holliday junction formed during bacterial homologous recombination.In Escherichia coli bacteria, DNA replication forks stall at least once per cell cycle, so that DNA replication must be restarted if the cell is to survive. [2]
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.
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 .
Crossover junction endonuclease MUS81 is an enzyme that in humans is encoded by the MUS81 gene. [5] [6] [7]In mammalian somatic cells, MUS81 and another structure specific DNA endonuclease, XPF (), play overlapping and essential roles in completion of homologous recombination. [8]