title: Fidelity of Escherichia coli DNA polymerase IV. Preferential generation of small deletion mutations by dNTP-stabilized misalignment.
abstract: Escherichia coli DNA polymerase IV (pol IV), a member of the error-prone Y family, predominantly generates -1 frameshifts when copying DNA in vitro. T-->G transversions and T-->C transitions are the most frequent base substitutions observed. The in vitro data agree with mutational spectra obtained when pol IV is overexpressed in vivo. Single base deletion and base substitution rates measured in the lacZalpha gene in vitro are, on average, 2 x 10(-4) and 5 x 10(-5), respectively. The range of misincorporation and mismatch extension efficiencies determined kinetically are 10(-3) to 10(-5). The presence of beta sliding clamp and gamma-complex clamp loading proteins strongly enhance pol IV processivity but have no discernible influence on fidelity. By analyzing changes in fluorescence of a 2-aminopurine template base undergoing replication in real time, we show that a "dNTP-stabilized" misalignment mechanism is responsible for making -1 frameshift mutations on undamaged DNA. In this mechanism, a dNTP substrate is paired "correctly" opposite a downstream template base, on a "looped out" template strand instead of mispairing opposite a next available template base. By using the same mechanism, pol IV "skips" past an abasic template lesion to generate a -1 frameshift. A crystal structure depicting dNTP-stabilized misalignment was reported recently for Sulfolubus solfataricus Dpo4, a Y family homolog of Escherichia coli pol IV.
authors.affiliation: Department of Biological Sciences and Chemistry, Hedco Molecular Biology Laboratories, University of Southern California, University Park, Los Angeles, CA 90089-1340, USA.
authors.forename: Sawami
authors.initials: S
authors.lastname: Kobayashi
authors.forename: Michael R
authors.initials: MR
authors.lastname: Valentine
authors.forename: Phuong
authors.initials: P
authors.lastname: Pham
authors.forename: Mike
authors.initials: M
authors.lastname: O'Donnell
authors.forename: Myron F
authors.initials: MF
authors.lastname: Goodman
mesh_terms: D020137:Base Pair Mismatch; D001483:Base Sequence; D002384:Catalysis; D019951:DNA Polymerase beta / Q000737:chemistry*; D003854:Deoxyribonucleotides / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins / Q000737:chemistry*; D016368:Frameshift Mutation; D008969:Molecular Sequence Data
chemical_list: D003854:Deoxyribonucleotides; D029968:Escherichia coli Proteins; C509838:Dpo4 protein, E coli; D019951:DNA Polymerase beta