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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 ...
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.
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.
Homologous recombination involves the exchange of DNA materials between homologous chromosomes. There are multiple pathways of HR to repair DSBs, which includes double-strand break repair (DSBR), synthesis-dependent strand annealing (SDSA), break-induced replication (BIR), and single-strand annealing (SSA).
Most recombination occurs naturally and can be classified into two types: (1) interchromosomal recombination, occurring through independent assortment of alleles whose loci are on different but homologous chromosomes (random orientation of pairs of homologous chromosomes in meiosis I); & (2) intrachromosomal recombination, occurring through ...
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]
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 ...