title: Alpha-anomeric deoxynucleotides, anoxic products of ionizing radiation, are substrates for the endonuclease IV-type AP endonucleases.
abstract: Alpha-anomeric 2'-deoxynucleosides (alphadN) are one of the products formed by ionizing radiation (IR) in DNA under anoxic conditions. Alpha-2'-deoxyadenosine (alphadA) and alpha-thymidine (alphaT) are not recognized by DNA glycosylases, and are likely removed by the alternative nucleotide incision repair (NIR) pathway. Indeed, it has been shown that alphadA is a substrate for the Escherichia coli Nfo and human Ape1 proteins. However, the repair pathway for removal of alphadA and other alphadN in yeast is unknown. Here we report that alphadA when present in DNA is recognized by the Saccharomyces cerevisiae Apn1 protein, a homologue of Nfo. Furthermore, alphaT is a substrate for Nfo and Apn1. Kinetic constants indicate that alphadA and alphaT are equally good substrates, as a tetrahydrofuranyl (THF) residue, for Nfo and Apn1. Using E. coli and S. cerevisiae cell-free extracts, we have further substantiated the role of the nfo and apn1 gene products in the repair of alphadN. Surprisingly, we found that bacteria and yeast NIR-deficient mutants are not sensitive to IR, suggesting that DNA strand breaks with terminal 3'-blocking groups rather than alphadN might contribute to cell survival. We propose that the novel substrate specificities of Nfo and Apn1 play an important role in counteracting oxidative DNA base damage.
authors.affiliation: Groupe Réparation de l'ADN, UMR 8126 CNRS, Institut Gustave Roussy, 94805 Villejuif Cedex, France.
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Ishchenko
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ide
authors.forename: Dindial
authors.initials: D
authors.lastname: Ramotar
authors.forename: Georgy
authors.initials: G
authors.lastname: Nevinsky
authors.forename: Murat
authors.initials: M
authors.lastname: Saparbaev
mesh_terms: D000693:Anaerobiosis / Q000235:genetics / Q000528:radiation effects; D020029:Base Pairing; D002474:Cell-Free System / Q000378:metabolism / Q000528:radiation effects; D004249:DNA Damage; D004260:DNA Repair / Q000528:radiation effects; D045643:DNA Repair Enzymes; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase / Q000737:chemistry* / Q000528:radiation effects; D003839:Deoxyadenosines / Q000737:chemistry* / Q000528:radiation effects; D043223:Deoxyribonuclease IV (Phage T4-Induced) / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D004706:Endodeoxyribonucleases / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics / Q000528:radiation effects; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D005720:Gamma Rays; D006801:Humans; D007700:Kinetics; D016296:Mutagenesis; D009692:Nucleic Acid Heteroduplexes / Q000737:chemistry / Q000235:genetics / Q000528:radiation effects; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics / Q000528:radiation effects; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D013379:Substrate Specificity / Q000235:genetics / Q000528:radiation effects; D013936:Thymidine / Q000378:metabolism / Q000528:radiation effects
chemical_list: D003839:Deoxyadenosines; D029968:Escherichia coli Proteins; D009692:Nucleic Acid Heteroduplexes; D029701:Saccharomyces cerevisiae Proteins; C003965:2'-amino-2'-deoxyadenosine; D004706:Endodeoxyribonucleases; D043223:Deoxyribonuclease IV (Phage T4-Induced); C468972:endonuclease IV, E coli; C083274:Apn1 protein, S cerevisiae; C085108:APEX1 protein, human; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase; D045643:DNA Repair Enzymes; D013936:Thymidine