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O6-alkyl guanine transferase II (O6 AGT II) previously known as O6 Guanine transferase (ogt) is also part of the DNA repair system along with Ada [1].

Like Ada, AGT II is responsible for the removal of alkyl groups from O6-alkyl guanine, O4-alkyl thymine and alkyl phosphotriester in the sugar-phosphate backbone of DNA.[1] AGT II shows a greater preference for O4-alkyl thymine than O6-alkyl guanine and alkyl phosphotriester. [1][2]

Unlike Ada, AGT II is expressed constitutively in cells.[1][3] Therefore, AGT II will repair alkylated DNA adducts even before Ada is fully induced. AGT II is similar to Ada in its suicide inactivation-- AGT II transfers the alkyl group to a cysteine residue in its own structure, thereby inactivating itself.[1] The human equivalent of AGT II is MGMT (O6-methyl guanine methyl transferase). MGMT preferentially removes alkyl groups from O6-alkyl guanine than from O4–alkyl thymine.[1]


  1. ^ a b c d e f Errol Friedberg, Graham C. Walker, Wolfram Siede, Richard D. Wood, Roger A. Schultz, Tom Ellenberger. DNA Repair and Mutagenesis, 2nd edition, ASM Press, ISBN 1-55581-319-4
  2. ^ Sassanfar M, Dosanjh MK, Essigmann JM, Samson L. 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. J Biol Chem. 1991 Feb 15;266(5):2767-71. PMID 1993655.
  3. ^ Rebeck GW, Samson L. Increased spontaneous mutation and alkylation sensitivity of Escherichia coli strains lacking the ogt O6-methylguanine DNA repair methyltransferase. J Bacteriol. 1991 Mar;173(6):2068-76. PMID 2002008.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Ogt". A list of authors is available in Wikipedia.
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