AGT II

{{Short description|Microbial protein found in Escherichia coli str. K-12 substr. MG1655}} {{Infobox nonhuman protein |Name=Methylated-DNA--protein-cysteine methyltransferase |Symbol=ogt |Organism=Escherichia coli |UniProt=P0AFH0 }} '''''O''⁶-alkylguanine DNA alkyltransferase II''' ('''''O''⁶ AGT II''') previously known as ''O''⁶ Guanine transferase (ogt) is an ''E. coli'' protein that is involved in DNA repair together with Ada ( also known as ''O''⁶ AGT I).<ref name="Friedberg">{{cite book | title = DNA Repair and Mutagenesis | edition = 2 | last1 = Friedberg | first1 = Errol | first2 = Graham C. | last2 = Walker | first3 = Wolfram | last3 = Siede | first4 = Richard D. | last4 = Wood | first5 = Roger A. | last5 = Schultz | first6 = Tom | last6 = Ellenberger | name-list-style = vanc | author-link4 = Richard D. Wood | year = 2006 | publisher=ASM Press | location = Washington, DC | isbn = 1-55581-319-4 | oclc = 59360087 }}</ref>

Like AGT I, AGT II is responsible for the removal of alkyl groups from ''O''⁶-alkyl guanine, ''O''⁴-alkyl thymine and alkyl phosphotriester in the sugar-phosphate backbone of DNA.<ref name="Friedberg"/> AGT II shows a greater preference for ''O''⁴-alkyl thymine than ''O''⁶-alkyl guanine and alkyl phosphotriester.<ref name="Friedberg"/><ref name="Sassanfar">{{cite journal | vauthors = Sassanfar M, Dosanjh MK, Essigmann JM, Samson L | title = Relative efficiencies of the bacterial, yeast, and human DNA methyltransferases for the repair of O6-methylguanine and O4-methylthymine. Suggestive evidence for O4-methylthymine repair by eukaryotic methyltransferases | journal = The Journal of Biological Chemistry | volume = 266 | issue = 5 | pages = 2767–71 | date = February 1991 | doi = 10.1016/S0021-9258(18)49912-7 | pmid = 1993655 | doi-access = free }}</ref>

Unlike Ada, AGT II is expressed constitutively in cells.<ref name="Friedberg"/><ref name="Rebeck">{{cite journal | vauthors = Rebeck GW, Samson L | title = Increased spontaneous mutation and alkylation sensitivity of Escherichia coli strains lacking the ogt O6-methylguanine DNA repair methyltransferase | journal = Journal of Bacteriology | volume = 173 | issue = 6 | pages = 2068–76 | date = March 1991 | doi = 10.1128/jb.173.6.2068-2076.1991 | pmid = 2002008 | pmc = 207742 }}</ref> Therefore, AGT II will repair alkylated DNA adducts even before Ada is fully induced. AGT II is similar to Ada in its suicide inactivation in that AGT II transfers the alkyl group to a cysteine residue in its own structure, thereby inactivating itself.<ref name="Friedberg"/> The human equivalent of AGT II is ''O''⁶-alkylguanine DNA alkyltransferase, a protein that in humans is encoded by the ''O''⁶-methylguanine DNA methyltransferase (''MGMT'') gene. In humans, ''O''⁶-alkylguanine DNA alkyltransferase preferentially removes alkyl groups from ''O''⁶-alkyl guanine rather than from ''O''⁶–alkyl thymine.<ref name="Friedberg"/>

== References == {{Reflist}}

Category:DNA repair

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