title: Opposite base specificity in excision of pyrimidine ring-opened 1,N6-ethenoadenine by thymine glycol-DNA-glycosylases.
abstract: A highly mutagenic DNA lesion, 1,N6-ethenoadenine ( epsilon A) is chemically unstable and either depurinates or converts to a pyrimidine ring-opened product upon water molecule addition to the C(2)z.sbnd;N(3) bond in epsilon dA (compound B). Compound B subsequently undergoes deformylation to yield compound C, which depurinates in the final step of the epsilon A rearrangement pathway. We have previously shown that epsilon A rearrangement products are not repaired by human N-methylpurine-DNA-glycosylase, which excises parental epsilon A. Compound B was shown to be eliminated from a B:T pair by Escherichia coli formamidopyrimidine-DNA-glycosylase (Fpg protein) and endonuclease III (Nth protein). Fpg protein excised B also from a B:C pair, and much less efficiently from B:A and B:G pairs [J. Biol. Chem. 276 (2001) 21821]. Here we show that efficiency of B excision by the Nth protein also depends on the opposite base in the pair. Most efficient repair is observed when this derivative is paired with dG (Km=18nM, kcat=12) and is less favourable when paired with dC (Km=40nM, kcat=13) and dT (Km=32nM, kcat=11). In physiological conditions, compound B is probably not excised by the Nth-glycosylase from a B:A pair, or from a single-stranded DNA, since kinetic constants in these conditions are an order or two orders of magnitude higher than when B is paired with T, C or G. A similar specificity for B excision was found for Saccharomyces cerevisiae Ntg2-glycosylase. Thus, when paired with A, an epsilon A derivative might be more persistent than when paired with other bases and give rise to AT-->TA transversions.
authors.affiliation: Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawińskiego 5A, 02-106, Warsaw, Poland.
authors.forename: Monika
authors.initials: M
authors.lastname: Bajek
authors.forename: Jarosław M
authors.initials: JM
authors.lastname: Cieśla
authors.forename: Barbara
authors.initials: B
authors.lastname: Tudek
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives* / Q000378:metabolism*; D004249:DNA Damage; D045647:DNA Glycosylases; D017931:DNA Primers / Q000737:chemistry; D004260:DNA Repair; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase; D043224:Deoxyribonuclease (Pyrimidine Dimer); D004706:Endodeoxyribonucleases / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D029968:Escherichia coli Proteins; D007700:Kinetics; D009699:N-Glycosyl Hydrolases / Q000378:metabolism*; D009838:Oligodeoxyribonucleotides / Q000737:chemistry / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins; D013936:Thymidine / Q000737:chemistry / Q000378:metabolism
chemical_list: D017931:DNA Primers; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D009838:Oligodeoxyribonucleotides; D029701:Saccharomyces cerevisiae Proteins; C007640:1,N(6)-ethenoadenosine; D004706:Endodeoxyribonucleases; D043224:Deoxyribonuclease (Pyrimidine Dimer); C106403:NTH protein, E coli; D045647:DNA Glycosylases; D009699:N-Glycosyl Hydrolases; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase; C116827:NTG2 protein, S cerevisiae; D000241:Adenosine; D013936:Thymidine