title: Enzymatic capture of an extrahelical thymine in the search for uracil in DNA.
abstract: The enzyme uracil DNA glycosylase (UNG) excises unwanted uracil bases in the genome using an extrahelical base recognition mechanism. Efficient removal of uracil is essential for prevention of C-to-T transition mutations arising from cytosine deamination, cytotoxic U*A pairs arising from incorporation of dUTP in DNA, and for increasing immunoglobulin gene diversity during the acquired immune response. A central event in all of these UNG-mediated processes is the singling out of rare U*A or U*G base pairs in a background of approximately 10(9) T*A or C*G base pairs in the human genome. Here we establish for the human and Escherichia coli enzymes that discrimination of thymine and uracil is initiated by thermally induced opening of T*A and U*A base pairs and not by active participation of the enzyme. Thus, base-pair dynamics has a critical role in the genome-wide search for uracil, and may be involved in initial damage recognition by other DNA repair glycosylases.
authors: Department of Pharmacology and Molecular Sciences, Johns Hopkins Medical School, 725 North Wolfe Street, Baltimore, Maryland 21205, USA.
authors: Jared B
authors: JB
authors: Parker
authors: Mario A
authors: MA
authors: Bianchet
authors: Daniel J
authors: DJ
authors: Krosky
authors: Joshua I
authors: JI
authors: Friedman
authors: L Mario
authors: LM
authors: Amzel
authors: James T
authors: JT
authors: Stivers
mesh_terms: D020029:Base Pairing; D001665:Binding Sites; D004247:DNA / Q000737:chemistry* / Q000378:metabolism*; D004249:DNA Damage; D004260:DNA Repair; D004926:Escherichia coli / Q000201:enzymology; D006801:Humans; D008958:Models, Molecular; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D009690:Nucleic Acid Conformation; D011487:Protein Conformation; D011522:Protons; D011743:Pyrimidines / Q000378:metabolism; D013379:Substrate Specificity; D013941:Thymine / Q000378:metabolism*; D014498:Uracil / Q000378:metabolism*; D051981:Uracil-DNA Glycosidase / Q000235:genetics / Q000378:metabolism*
chemical_list: D050505:Mutant Proteins; D011522:Protons; D011743:Pyrimidines; D014498:Uracil; D004247:DNA; D051981:Uracil-DNA Glycosidase; C030986:pyrimidine; D013941:Thymine
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