title: Isolation of cDNA clones encoding an enzyme from bovine cells that repairs oxidative DNA damage in vitro: homology with bacterial repair enzymes.
abstract: Ionizing radiation and radiomimetic compounds, such as hydrogen peroxide and bleomycin, generate DNA strand breaks with fragmented deoxyribose 3' termini via the formation of oxygen-derived free radicals. These fragmented sugars require removal by enzymes with 3' phosphodiesterase activity before DNA synthesis can proceed. An enzyme that reactivates bleomycin-damaged DNA to a substrate for Klenow polymerase has been purified from calf thymus. The enzyme, which has a Mr of 38,000 on SDS-PAGE, also reactivates hydrogen peroxide-damaged DNA and has an associated apurinic/apyrimidinic (AP) endonuclease activity. The N-terminal amino acid sequence of the purified protein matches that reported previously for a calf thymus enzyme purified on the basis of AP endonuclease activity. Degenerate oligonucleotide primers based on this sequence were used in the polymerase chain reaction to generate from a bovine cDNA library a fragment specific for the 5' end of the coding sequence. Using this cDNA fragment as a probe, several clones containing 1.35 kb cDNA inserts were isolated and the complete nucleotide sequence of one of these determined. This revealed an 0.95 kb open reading frame which would encode a polypeptide of Mr 35,500 and with a N-terminal sequence matching that determined experimentally. The predicted amino acid sequence shows strong homology with the sequences of two bacterial enzymes that repair oxidative DNA damage, ExoA protein of S. pneumoniae and exonuclease III of E. coli.
authors.affiliation: Imperial Cancer Research Fund, Institute of Molecular Medicine, John Radcliffe Hospital, Oxford, UK.
authors.forename: C N
authors.initials: CN
authors.lastname: Robson
authors.forename: A M
authors.initials: AM
authors.lastname: Milne
authors.forename: D J
authors.initials: DJ
authors.lastname: Pappin
authors.forename: I D
authors.initials: ID
authors.lastname: Hickson
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001761:Bleomycin / Q000494:pharmacology; D002417:Cattle; D003001:Cloning, Molecular; D004247:DNA / Q000302:isolation & purification; D004249:DNA Damage; D004260:DNA Repair; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase; D004259:DNA-Directed DNA Polymerase / Q000378:metabolism; D043223:Deoxyribonuclease IV (Phage T4-Induced); D004591:Electrophoresis, Polyacrylamide Gel; D004706:Endodeoxyribonucleases / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D005092:Exonucleases / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000494:pharmacology; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D010084:Oxidation-Reduction; D016415:Sequence Alignment; D013950:Thymus Gland / Q000201:enzymology
chemical_list: D001761:Bleomycin; D004247:DNA; D006861:Hydrogen Peroxide; D004259:DNA-Directed DNA Polymerase; D004706:Endodeoxyribonucleases; D005092:Exonucleases; D043223:Deoxyribonuclease IV (Phage T4-Induced); D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase