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.

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. AGT II shows a greater preference for O4-alkyl thymine than O6-alkyl guanine and alkyl phosphotriester.

Unlike Ada, AGT II is expressed constitutively in cells. 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. 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.