Ogt

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].

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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]

References

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.