title: [O6-benzylguanine stimulates regulatory functions of the Ada protein in Escherichia coli].
abstract: In vitro experiments showed that O6-benzylguanine (O6-benzG, 0.2 microM) fully inhibited the repair activity of human O6-alkylguanine-DNA alkyltransferase (MGMT) due to the formation of S-benzylcytosine in the protein acceptor site. O6-benzG at concentrations increased many times (up to 800 microM) failed to inhibit the repair activity of the Escherichia coli Ada protein, the structural and functional analog of MGMT. It has been shown for the first time that O6-benzG stimulates the regulatory activity of the Ada protein. In experiments with N-nitroso-N-methylurea (NMU), the pretreatment of Escherichia coli cells with O6-benzG at a sublethal concentration of 10 microM led to a twofold enhancement of transcription at the Ada-dependent promoter of the alkA gene in control cells and ensured transcription enhanced 1.6-1.7 times at alkA and alkB promoters in cells with the induced "classical" Ada response. Apparently, an increase in the regulatory activity of the Ada protein was associated with the formation of the stable protein molecule having the strong affinity for alkA and alkB promoters after transfer of the benzyl group from O6-benzG to the acceptor site Cys-69 in the N-terminal domain of Ada protein. O6-benzG did not affect the regulative activity of Ada in alternative quasi-adaptive responses to NMU.
authors.forename: S V
authors.initials: SV
authors.lastname: Vasil'eva
authors.forename: E Iu
authors.initials: EIu
authors.lastname: Moshkovskaia
authors.forename: I G
authors.initials: IG
authors.lastname: Kosenko
mesh_terms: D045647:DNA Glycosylases / Q000096:biosynthesis; D004260:DNA Repair / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000096:biosynthesis / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D006147:Guanine / Q000031:analogs & derivatives* / Q000494:pharmacology; D006801:Humans; D006899:Mixed Function Oxygenases / Q000096:biosynthesis; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D014157:Transcription Factors / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D029968:Escherichia coli Proteins; D014157:Transcription Factors; C064976:O(6)-benzylguanine; D006147:Guanine; D006899:Mixed Function Oxygenases; C466427:AlkB protein, E coli; C045675:Ada protein, E coli; D019853:O(6)-Methylguanine-DNA Methyltransferase; D045647:DNA Glycosylases; C076131:DNA-3-methyladenine glycosidase II