title: Efficient removal of uracil from G.U mispairs by the mismatch-specific thymine DNA glycosylase from HeLa cells.
abstract: The uracil DNA glycosylases (EC 3.2.2.3) characterized to date remove uracil from DNA irrespective of whether it is base paired with adenine or mispaired with guanine in double-stranded substrates or whether it is found in single-stranded DNA. We report here the characterization of uracil glycosylase activity that can remove the base solely from a mispair with guanine. It does not recognize uracil either in A.U pairs or in single-stranded substrates. The enzyme, a 55-kDa polypeptide, was previously characterized as a mismatch-specific thymine DNA glycosylase and was thought to be responsible solely for the correction (to G.C) of G.T mispairs that arise as a result of spontaneous hydrolytic deamination of 5-methylcytosine to thymine. Given the broader substrate specificity of the enzyme (in addition to uracil and thymine, the protein can also remove 5-bromouracil from mispairs with guanine), we propose that its biological role in vivo may also include the correction of a subset of G.U mispairs inefficiently removed by the more abundant ubiquitous uracil glycosylases, such as those arising from cytosine deamination in G+C-rich regions of the genome.
authors.affiliation: Department of Biochemistry, Istituto di Richerche di Biologia Molecolare P. Angeletti, Pomezia, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Neddermann
authors.forename: J
authors.initials: J
authors.lastname: Jiricny
mesh_terms: D001482:Base Composition; D001483:Base Sequence; D004247:DNA / Q000235:genetics* / Q000378:metabolism*; D004260:DNA Repair / Q000502:physiology*; D043224:Deoxyribonuclease (Pyrimidine Dimer); D004706:Endodeoxyribonucleases / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D013379:Substrate Specificity; D013941:Thymine; D014498:Uracil
chemical_list: D014498:Uracil; D004247:DNA; D004706:Endodeoxyribonucleases; D043224:Deoxyribonuclease (Pyrimidine Dimer); D013941:Thymine