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Nucleotide excision repair is more complex in eukaryotes than prokaryotes, which express enzymes like the photolyase. In humans and other placental animals , there are 9 major proteins involved in NER.
Base excision repair (BER): damaged single bases or nucleotides are most commonly repaired by removing the base or the nucleotide involved and then inserting the correct base or nucleotide. In base excision repair, a glycosylase [ 22 ] enzyme removes the damaged base from the DNA by cleaving the bond between the base and the deoxyribose.
The system involves the RecA protein (Rad51 in eukaryotes). The RecA protein, stimulated by single-stranded DNA, is involved in the inactivation of the repressor of SOS response genes thereby inducing the response. It is an error-prone repair system that contributes significantly to DNA changes observed in a wide range of species.
Basic steps of base excision repair. Base excision repair (BER) is a cellular mechanism, studied in the fields of biochemistry and genetics, that repairs damaged DNA throughout the cell cycle. It is responsible primarily for removing small, non-helix-distorting base lesions from the genome. The related nucleotide excision repair pathway repairs
Replication protein A (RPA) is the major protein that binds to single-stranded DNA (ssDNA) in eukaryotic cells. [1] [2] In vitro, RPA shows a much higher affinity for ssDNA than RNA or double-stranded DNA. [3] RPA is required in replication, recombination and repair processes such as nucleotide excision repair and homologous recombination.
In eukaryotes, MutS homologs form two major heterodimers: Msh2/Msh6 (MutSα) and Msh2/Msh3 (MutSβ). The MutSα pathway is involved primarily in base substitution and small-loop mismatch repair. The MutSβ pathway is also involved in small-loop repair, in addition to large-loop (~10 nucleotide loops) repair.
The complex of XPC-RAD23B is the initial damage recognition factor in global genomic nucleotide excision repair (GG-NER). XPC-RAD23B recognizes a wide variety of lesions that thermodynamically destabilize DNA duplexes, including UV-induced photoproducts (cyclopyrimidine dimers and 6-4 photoproducts ), adducts formed by environmental mutagens such as benzo[a]pyrene or various aromatic amines ...
Most DNA repair processes form single-strand gaps in DNA during an intermediate stage of the repair, and these gaps are filled in by repair synthesis. [4] The specific repair processes that require gap filling by DNA synthesis include nucleotide excision repair , base excision repair , mismatch repair , homologous recombinational repair, non ...