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These altered bases arise from the frequent hydrolysis of cytosine to uracil (see image) and hydrolysis of 5-methylcytosine to thymine, producing G:U and G:T base pairs. [29] If the improper uracils or thymines in these base pairs are not removed before DNA replication, they will cause transition mutations .
It acts as a 3’→5’ DNA directed proofreading exonuclease that removes incorrectly incorporated bases during replication. [10] Similarly, in Salmonella typhimurium bacteria, the 3’ to 5’ editing function employed during DNA replication is also encoded by a gene, dnaQ , which specifies a 3’ to 5’ exonuclease subunit, one of the ...
dnaQ is the gene encoding the ε subunit of DNA polymerase III in Escherichia coli. [1] The ε subunit is one of three core proteins in the DNA polymerase complex. It functions as a 3’→5’ DNA directed proofreading exonuclease that removes incorrectly incorporated bases during replication.
8-oxoguanine forms a Hoogsteen base pair with adenine. Single bases in DNA can be chemically damaged by a variety of mechanisms, the most common ones being deamination, oxidation, and alkylation. These modifications can affect the ability of the base to hydrogen-bond, resulting in incorrect base-pairing, and, as a consequence, mutations in the DNA.
MUTYH has its locus on the short (p) arm of chromosome 1 (1p34.1), from base pair 45,464,007 to base pair 45,475,152 (45,794,835–45,806,142). The gene is composed of 16 exons and has a size of 546 amino acids [6] and is approximately 7.1kb. [7] The presence of disulfide crosslinking gives rise to a complex crystal structure of the MUTY-DNA. [8]
When an incorrect base pair is recognized, DNA polymerase moves backwards by one base pair of DNA. The 3'–5' exonuclease activity of the enzyme allows the incorrect base pair to be excised (this activity is known as proofreading). Following base excision, the polymerase can re-insert the correct base and replication can continue forwards.
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.
Apurinic/apyrimidinic (AP) endonuclease is an enzyme that is involved in the DNA base excision repair pathway (BER). Its main role in the repair of damaged or mismatched nucleotides in DNA is to create a nick in the phosphodiester backbone of the AP site created when DNA glycosylase removes the damaged base.