title: DNA polymerase iota-dependent translesion replication of uracil containing cyclobutane pyrimidine dimers.
abstract: Analysis of the spectrum of UV-induced mutations generated in synchronized wild-type S-phase cells reveals that only approximately 25% of mutations occur at thymine (T), whilst 75% are targeted to cytosine (C). The mutational spectra changes dramatically in XP-V cells, devoid of poleta, where approximately 45% of mutations occur at Ts and approximately 55% at Cs. At the present time, it is unclear whether the C-->T mutations actually represent true misincorporations opposite C, or perhaps occur as the result of the correct incorporation of adenine (A) opposite a C in a UV-photoproduct that had undergone deamination to uracil (U). In order to assess the role that human poliota might play, if any, in the replicative bypass of such UV-photoproducts, we have analyzed the efficiency and fidelity of pol iota-dependent bypass of a T-U cyclobutane pyrimidine dimer (CPD) in vitro. Interestingly, pol iota-dependent bypass of a T-U CPD occurs more efficiently than that of a corresponding T-T CPD. Guanine (G) was misincorporated opposite the 3'U of the T-U CPD only two-fold less frequently than the correct Watson-Crick base, A. While pol iota generally extended the G:3'U-CPD mispairs less efficiently than the correctly paired primer, pol iota-dependent extension was equal to, or greater than that observed with human pols eta and kappa and S. cerevisiae pol zeta under the same assay conditions. Thus, we hypothesize that the ability of pol iota to bypass T-U CPDs through the frequent misincorporation of G opposite the 3'U of the CPD, may provide a mechanism whereby human cells can decrease the mutagenic potential of these lesions.
authors.affiliation: Section on DNA Replication, Repair, and Mutagenesis, Laboratory of Genomic Integrity, Building 6, Room 1A13, National Institute of Child Health and Human Development, National Institutes of Health, 9000 Rockville Pike, Bethesda, MD 20892-2725, USA.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Vaisman
authors.forename: Kohei
authors.initials: K
authors.lastname: Takasawa
authors.forename: Shigenori
authors.initials: S
authors.lastname: Iwai
authors.forename: Roger
authors.initials: R
authors.lastname: Woodgate
mesh_terms: D002273:Carcinogens; D002384:Catalysis; D004249:DNA Damage; D017931:DNA Primers / Q000737:chemistry; D004260:DNA Repair; D004261:DNA Replication; D004259:DNA-Directed DNA Polymerase / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics; D007700:Kinetics; D009153:Mutagens; D009154:Mutation; D011740:Pyrimidine Dimers / Q000737:chemistry*; D013997:Time Factors; D014466:Ultraviolet Rays; D014498:Uracil / Q000737:chemistry*; D014983:Xeroderma Pigmentosum / Q000235:genetics; D000094769:DNA Polymerase iota
chemical_list: D002273:Carcinogens; D017931:DNA Primers; D009153:Mutagens; D011740:Pyrimidine Dimers; D014498:Uracil; D007041:Hypoxanthine Phosphoribosyltransferase; D005982:Glutathione Transferase; D004259:DNA-Directed DNA Polymerase; D000094769:DNA Polymerase iota; C000722070:POLI protein, human