Enzymatic capture of an extrahelical thymine in the search for uracil in DNA.
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.
Parker
Jared B
JB
Department of Pharmacology and Molecular Sciences, Johns Hopkins Medical School, 725 North Wolfe Street, Baltimore, Maryland 21205, USA.
Bianchet
Mario A
MA
Krosky
Daniel J
DJ
Friedman
Joshua I
JI
Amzel
L Mario
LM
Stivers
James T
JT
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*
D050505:Mutant Proteins; D011522:Protons; D011743:Pyrimidines; D014498:Uracil; D004247:DNA; D051981:Uracil-DNA Glycosidase; C030986:pyrimidine; D013941:Thymine
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