Open AccessActive site and complete sequence of the suicidal methyltransferase that counters alkylation mutagenesis.
Author(s) -
Bruce Demple,
Barbara Sedgwick,
Peter Robins,
Nicholas F. Totty,
Mike Waterfield,
Tomas Lindahl
Publication year - 1985
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.82.9.2688
Subject(s) - mutagenesis , biology , cysteine , dna , methyltransferase , biochemistry , dna methyltransferase , site directed mutagenesis , active site , dna repair , o 6 methylguanine dna methyltransferase , peptide sequence , gene , microbiology and biotechnology , mutation , chemistry , enzyme , methylation , mutant
The inducible resistance to alkylation mutagenesis and killing in Escherichia coli (the adaptive response) is controlled by the ada gene. The Ada protein acts both as a positive regulator of the response and as a DNA repair enzyme, correcting premutagenic O6-alkylguanine in DNA by suicidal transfer of the alkyl group to one of its own cysteine residues. We have determined the DNA sequence of the cloned ada+ gene and its regulatory region. The data reveal potential sites of ada autoregulation. Amino acid sequence determinations show that the active center for the O6-methylguanine-DNA methyltransferase is located close to the polypeptide COOH terminus and has the unusual sequence -Pro-Cys-His-, preceded by a very hydrophobic region. These same structural features are present at the active site of thymidylate synthase, suggesting a common chemical mechanism for activation of the cysteine.