title: Replication infidelity via a mismatch with Watson-Crick geometry.
abstract: In describing the DNA double helix, Watson and Crick suggested that "spontaneous mutation may be due to a base occasionally occurring in one of its less likely tautomeric forms." Indeed, among many mispairing possibilities, either tautomerization or ionization of bases might allow a DNA polymerase to insert a mismatch with correct Watson-Crick geometry. However, despite substantial progress in understanding the structural basis of error prevention during polymerization, no DNA polymerase has yet been shown to form a natural base-base mismatch with Watson-Crick-like geometry. Here we provide such evidence, in the form of a crystal structure of a human DNA polymerase λ variant poised to misinsert dGTP opposite a template T. All atoms needed for catalysis are present at the active site and in positions that overlay with those for a correct base pair. The mismatch has Watson-Crick geometry consistent with a tautomeric or ionized base pair, with the pH dependence of misinsertion consistent with the latter. The results support the original idea that a base substitution can originate from a mismatch having Watson-Crick geometry, and they suggest a common catalytic mechanism for inserting a correct and an incorrect nucleotide. A second structure indicates that after misinsertion, the now primer-terminal G • T mismatch is also poised for catalysis but in the wobble conformation seen in other studies, indicating the dynamic nature of the pathway required to create a mismatch in fully duplex DNA.
authors.affiliation: Laboratory of Molecular Genetics, Department of Health and Human Services, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA.
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Bebenek
authors.forename: Lars C
authors.initials: LC
authors.lastname: Pedersen
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Kunkel
mesh_terms: D020137:Base Pair Mismatch; D018360:Crystallography, X-Ray; D004247:DNA / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D009690:Nucleic Acid Conformation
chemical_list: D004247:DNA