title: Metal dependence of transcriptional switching in Escherichia coli Ada.
abstract: The Escherichia coli Ada protein repairs methylphosphotriesters in DNA by direct, irreversible methyl transfer to one of its own cysteine residues. The methyl transfer process is autocatalyzed by coordination of the acceptor residue, Cys69, to a tightly bound zinc ion. Kinetic data reveal a 4-fold reduction in the methylphosphotriester repair activity for the Cd(II) form of Ada versus the native Zn(II)-bound form, thus confirming a direct role for the metal in autocatalysis. Quantitative electrophoretic mobility shift assays reveal that the specific DNA affinity of the protein is increased 10(3)-fold by transfer of a methyl group to Cys69; the Cd(II) and the Zn(II) forms of the protein behave similarly in this respect. This methylation-sensitive stimulation of binding underlies the ability of Ada to activate inducibly the transcription of a methylation-dependent regulon. We conclude that the chemical properties of the bound metal influence the transition state for autocatalytic methyl transfer, but not the structure that ultimately results from this process.
authors.affiliation: Program for Higher Degrees in Biophysics, Harvard University, Cambridge, Massachusetts 02138.
authors.forename: L C
authors.initials: LC
authors.lastname: Myers
authors.forename: F
authors.initials: F
authors.lastname: Jackow
authors.forename: G L
authors.initials: GL
authors.lastname: Verdine
mesh_terms: D001426:Bacterial Proteins / Q000502:physiology*; D001483:Base Sequence; D004247:DNA / Q000378:metabolism; D004260:DNA Repair; D029968:Escherichia coli Proteins; D007700:Kinetics; D008670:Metals / Q000494:pharmacology*; D008745:Methylation; D008780:Methyltransferases / Q000502:physiology*; D008969:Molecular Sequence Data; D019853:O(6)-Methylguanine-DNA Methyltransferase; D014157:Transcription Factors; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D008670:Metals; D014157:Transcription Factors; D004247:DNA; D008780:Methyltransferases; C045675:Ada protein, E coli; D019853:O(6)-Methylguanine-DNA Methyltransferase