Ada Background Information Regulatory protein of adaptative response (Ada) is a monomeric, globular, 353 amino acid E. coli protein that functions in the repair of alkylated guanine in DNA. Ada has two alkylacceptor activities located in two nearly equally sized domains. Ada stoichiometrically accepts the alkyl group from the O-6 position of alkylguanine in DNA at cysteine residue 321 and from alkyl phosphotriester at cysteine residue 69. This reaction irreversibly inactivates the enzyme. Additionally, Ada can repair O-4-methylthymine. The N-terminus of Ada contains a region utilized in the activation of transcription of ALKA, ALKB, and AIDB.
