User:Xiang Chen/Sandbox 10: Difference between revisions

== Function ==

All three TET enzymes and their isoforms are involved in the biochemical pathway that converts 5-methylcytosine (5mC) into 5-hydroxymethylcytosine (5hmC). They also regulate the further conversions of 5hmC to 5-formylcytosine (5fC) and then 5fC to 5-carboxylcytosine (5caC).<ref name='He et al.'>DOI: 10.1126/science.1210944</ref> Although experimental data shows that TET3 does so to a lesser extent than TET1 and TET2.<ref name='He et al.' />

While the oxidation performed by TET enzymes was originally thought to be a source of DNA damage, new research has implied that this catalytic activity may actually be the initial steps of a process of DNA demethylation. This hypothesized DNA demethylation pathway starts with the conversion of 5mC to 5caC after several rounds of oxidation by TET enzymes. The next step is the removal of the modified cytosine base by thymine DNA glycosylase (TDG) which leaves an abasic site on the DNA. The last step is then the process of base excision repair in which a new unmodified cytosine is regenerated at the site, thus completing the process of DNA demethylation.<ref name='He et al.' /><ref name='Rahul M. Kohli & Yi Zhang'>DOI 10.1038/nature12750</ref>

Experimental data shows that the TET genes have different expression patterns and at different levels, which indicates that each of the TET enzymes do not fully overlap in their functionality.