title: Effects of a guanine-derived formamidopyrimidine lesion on DNA replication: translesion DNA synthesis, nucleotide insertion, and extension kinetics.
abstract: 2,6-Diamino-4-hydroxy-5-formamidopyrimidine derived from guanine (FapyG) is a major DNA lesion formed by reactive oxygen species. In this study, a defined oligonucleotide template containing a 5-N-methylated analog of FapyG (mFapyG) was prepared, and its effect on DNA replication was quantitatively assessed in vitro. The results were further compared with those obtained for 7,8-dihydro-8-oxoguanine and an apurinic/apyrimidinic site embedded in the same sequence context. mFapyG constituted a fairly strong but not absolute block to DNA synthesis catalyzed by Escherichia coli DNA polymerase I Klenow fragment with and without an associated 3'-5' exonuclease activity, thereby permitting translesion synthesis with a limited efficiency. The efficiency of translesion synthesis was G > 7,8-dihydro-8-oxoguanine > mFapyG > apurinic/apyrimidinic site. Analysis of the nucleotide insertion (f(ins) = V(max)/K(m) for insertion) and extension (f(ext) = V(max)/K(m) for extension) efficiencies for mFapyG revealed that the extension step constituted a major kinetic barrier to DNA synthesis. When mFapyG was bypassed, dCMP, a cognate nucleotide, was preferentially inserted opposite the lesion (dCMP (relative f(ins) = 1) dTMP (2.4 x 10(-4)) approximately dAMP (8.1 x 10(-5)) > dGMP (4.5 x 10(-7))), and the primer terminus containing a mFapyG:C pair was most efficiently extended (mFapyG:C (relative f(ext) = 1) > mFapyG:T (4.6 x 10(-3)) mFapyG:A and mFapyG:G (extension not observed)). Thus, mFapyG is a potentially lethal but not premutagenic lesion.
authors.affiliation: Department of Mathematical and Life Sciences, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan.
authors.forename: Kenjiro
authors.initials: K
authors.lastname: Asagoshi
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Terato
authors.forename: Yoshihiko
authors.initials: Y
authors.lastname: Ohyama
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ide
mesh_terms: D001483:Base Sequence; D004249:DNA Damage; D017931:DNA Primers; D004261:DNA Replication; D006147:Guanine / Q000378:metabolism*; D006358:Hot Temperature; D007700:Kinetics; D011743:Pyrimidines / Q000378:metabolism*
chemical_list: D017931:DNA Primers; D011743:Pyrimidines; C071023:2,6-diamino-4-hydroxy-5-formamidopyrimidine; D006147:Guanine