Ada (protein)

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Ada, also called as O6 alkyl guanine transferase I (O6 AGT I), is an enzyme induced by treatment of bacterial cells with alkylating agents that mainly cause methylation damage. This phenomenon is called the adaptive response hence the name . Ada transfers the alkyl group from DNA bases and sugar-phosphate backbone to a cysteine residue, inactivating itself. Consequently, it reacts stoichiometrically with its substrate rather than catalytically and is referred to as a suicide enzyme. Methylation of Ada protein converts it into a self transcriptional activator, inducing its own gene expression and the expression of other genes which together with Ada help the cells repair alkylation damage.[1] Ada removes the alkyl group attached to DNA bases like guanine (O6-alkyl guanine) or thymine (O4-alkyl thymine) and to the oxygen of the phosphodiester backbone of the DNA.[2][3] However, Ada shows greater preference for O6- alkyl guanine compared to either O4-thymine and alkylated phosphotriesters. Ada enzyme has two active sites, one for the alkylated guanines and thymines and the other for alkylated phosphotriesters.[1]

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  1. ^ a b Lindahl T, Sedgwick B, Sekiguchi M, Nakabeppu Y (1988). "Regulation and expression of adaptive response to alkylating agents" (PDF, fee required). Annu Rev Biochem. 57 (1): 133–57. doi:10.1146/ PMID 3052269. Retrieved 2009-02-10. 
  2. ^ Friedberg, Errol; Graham C. Walker; Wolfram Siede; Richard D. Wood; Roger A. Schultz; Tom Ellenberger (2006). DNA Repair and Mutagenesis (2 ed.). Washington, DC: ASM Press. ISBN 1-55581-319-4. OCLC 59360087. 
  3. ^ McCarthy TV, Lindahl T (1985). "Methyl phosphotriesters in alkylated DNA are repaired by the Ada regulatory protein of E. coli" (PDF). Nucleic Acids Res. 13 (8): 2683–98. doi:10.1093/nar/13.8.2683. PMC 341187Freely accessible. PMID 2987862.