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西亚试剂:Enzymatic capture of an extrahelical thymine in the search

Enzymatic capture of an extrahelical thymine in the search for uracil in DNA

Jared B. Parker1, Mario A. Bianchet2, Daniel J. Krosky1, Joshua I. Friedman1, L. Mario Amzel2 & James T. Stivers1

  1. Departments of Pharmacology and Molecular Sciences and,
  2. Biophysics and Biophysical Chemistry of the Johns Hopkins Medical School, 725 North Wolfe Street, Baltimore, Maryland 21205, USA

Correspondence to: James T. Stivers1 Correspondence and requests for materials should be addressed to J.T.S. (Email: jstivers@jhmi.edu).

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 Ufilled circleA 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 Ufilled circleA or Ufilled circleG base pairs in a background of approximately 109 Tfilled circleA or Cfilled circleG 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 Tfilled circleA and Ufilled circleA 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