Editing Deamination (section)

===5-methylcytosine===
Spontaneous deamination of [[5-methylcytosine]] results in [[thymine]] and ammonia. This is the most common single nucleotide mutation. In DNA, this reaction, if detected prior to passage of the replication fork, can be corrected by the enzyme [[thymine-DNA glycosylase]], which removes the thymine base in a G/T mismatch. This leaves an abasic site that is repaired by AP endonucleases and polymerase, as with uracil-DNA glycosylase.<ref>{{Cite journal |doi= 10.1074/jbc.271.22.12767 |title= Cloning and Expression of Human G/T Mismatch-specific Thymine-DNA Glycosylase |journal= Journal of Biological Chemistry |volume= 271 |issue= 22 |pages= 12767–74 |year= 1996 |last1= Gallinari |first1= P. |pmid=8662714|doi-access= free }}</ref>

==== Cytosine deamination increases C-To-T mutations ====
A known result of cytosine methylation is the increase of C-to-T transition mutations through the process of deamination. Cytosine deamination can alter the genome's many regulatory functions; previously silenced [[transposable element]]s (TEs) may become transcriptionally active due to the loss of CPG sites.<ref name=":0">{{Cite journal|last1=Zhou|first1=Wanding|last2=Liang|first2=Gangning|last3=Molloy|first3=Peter L.|last4=Jones|first4=Peter A.|date=11 August 2020|title=DNA methylation enables transposable element-driven genome expansion|journal=Proceedings of the National Academy of Sciences of the United States of America|volume=117|issue=32|pages=19359–19366|doi=10.1073/pnas.1921719117|issn=1091-6490|pmc=7431005|pmid=32719115|bibcode=2020PNAS..11719359Z |doi-access=free }}</ref> TEs have been proposed to accelerate the mechanism of enhancer creation by providing extra DNA that is compatible with the host transcription factors that eventually have an impact on C-to-T mutations.<ref name=":0" />