text: This response was first identified in E. coli.  The E. coli adaptive response constitutes of four genes: ada, alkA, alkB, and aidB, each one working in specific residues, all regulated by the E. coli  Ada protein.
  The E. coli adaptive response is mediated by the Ada protein, which covalently transfers methylation damage from DNA to one of its two active methyl acceptor cysteine residues: Cys38 and Cys321. The Ada protein can repair damage by transferring methyl groups from O6-methylguanine or O4-methylthymine to Cys321 and also from methylphosphotriesters to Cys38 residue through an irreversible process. It can also convert the protein from a weak to a strong activator of transcription, increasing alkylation repair activity.