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Nucleic Acids Res. 2016 Sep 30;44(17):8229-40. doi: 10.1093/nar/gkw556. Epub 2016 Jun 20.

Strand displacement synthesis by yeast DNA polymerase ε.

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Department of Medical Biochemistry and Biophysics, Umeå University, SE-90187 Umeå, Sweden Howard Hughes Medical Institute, Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, NY 10016, USA.
Department of Microbiology and Molecular Genetics, University of California, Davis, CA 95616-8665, USA.
Department of Medical Biochemistry and Biophysics, Umeå University, SE-90187 Umeå, Sweden


DNA polymerase ε (Pol ε) is a replicative DNA polymerase with an associated 3'-5' exonuclease activity. Here, we explored the capacity of Pol ε to perform strand displacement synthesis, a process that influences many DNA transactions in vivo We found that Pol ε is unable to carry out extended strand displacement synthesis unless its 3'-5' exonuclease activity is removed. However, the wild-type Pol ε holoenzyme efficiently displaced one nucleotide when encountering double-stranded DNA after filling a gap or nicked DNA. A flap, mimicking a D-loop or a hairpin structure, on the 5' end of the blocking primer inhibited Pol ε from synthesizing DNA up to the fork junction. This inhibition was observed for Pol ε but not with Pol δ, RB69 gp43 or Pol η. Neither was Pol ε able to extend a D-loop in reconstitution experiments. Finally, we show that the observed strand displacement synthesis by exonuclease-deficient Pol ε is distributive. Our results suggest that Pol ε is unable to extend the invading strand in D-loops during homologous recombination or to add more than two nucleotides during long-patch base excision repair. Our results support the hypothesis that Pol ε participates in short-patch base excision repair and ribonucleotide excision repair.

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