title: Active site mutations in mammalian DNA polymerase delta alter accuracy and replication fork progression.
abstract: DNA polymerase δ (pol δ) is one of the two main replicative polymerases in eukaryotes; it synthesizes the lagging DNA strand and also functions in DNA repair. In previous work, we demonstrated that heterozygous expression of the pol δ L604G variant in mice results in normal life span and no apparent phenotype, whereas a different substitution at the same position, L604K, is associated with shortened life span and accelerated carcinogenesis. Here, we report in vitro analysis of the homologous mutations at position Leu-606 in human pol δ. Four-subunit human pol δ variants that harbor or lack 3' → 5'-exonucleolytic proofreading activity were purified from Escherichia coli. The pol δ L606G and L606K holoenzymes retain catalytic activity and processivity similar to that of wild type pol δ. pol δ L606G is highly error prone, incorporating single noncomplementary nucleotides at a high frequency during DNA synthesis, whereas pol δ L606K is extremely accurate, with a higher fidelity of single nucleotide incorporation by the active site than that of wild type pol δ. However, pol δ L606K is impaired in the bypass of DNA adducts, and the homologous variant in mouse embryonic fibroblasts results in a decreased rate of replication fork progression in vivo. These results indicate that different substitutions at a single active site residue in a eukaryotic polymerase can either increase or decrease the accuracy of synthesis relative to wild type and suggest that enhanced fidelity of base selection by a polymerase active site can result in impaired lesion bypass and delayed replication fork progression.
authors.affiliation: Department of Biochemistry, University of Washington School of Medicine, Seattle, Washington 98195, USA.
authors.forename: Michael W
authors.initials: MW
authors.lastname: Schmitt
authors.forename: Ranga N
authors.initials: RN
authors.lastname: Venkatesan
authors.forename: Marie-Jeanne
authors.initials: MJ
authors.lastname: Pillaire
authors.forename: Jean-Sébastien
authors.initials: JS
authors.lastname: Hoffmann
authors.forename: Julia M
authors.initials: JM
authors.lastname: Sidorova
authors.forename: Lawrence A
authors.initials: LA
authors.lastname: Loeb
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D020134:Catalytic Domain / Q000235:genetics*; D004258:DNA Polymerase III / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004261:DNA Replication; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D018809:Proliferating Cell Nuclear Antigen; D020033:Protein Isoforms; D004258:DNA Polymerase III