O⁶-alkylguanine DNA alkyltransferase II (O⁶ AGT II) previously known as O⁶ Guanine transferase (ogt) is a bacterial protein that is involved in DNA repair together with Ada ( also known as O⁶ AGT I).^[1]

Like AGT I, 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 in that 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 O⁶-alkylguanine DNA alkyltransferase, a protein that in humans is encoded by the O⁶-methylguanine DNA methyltransferase (MGMT) gene. In humans, O⁶-alkylguanine DNA alkyltransferase preferentially removes alkyl groups from O⁶-alkyl guanine rather than from O⁶–alkyl thymine.^[1]