Functional interaction between the Werner Syndrome protein and DNA polymerase δ

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Abstract
Werner Syndrome (WS) is an inherited disease characterized by premature onset of aging, increased cancer incidence, and genomic instability. The WS gene encodes a 1,432-amino acid polypeptide (WRN) with a central domain homologous to the RecQ family of DNA helicases. Purified WRN unwinds DNA with 3′→5′ polarity, and also possesses 3′→5′ exonuclease activity. Elucidation of the physiologic function(s) of WRN may be aided by the identification of WRN-interacting proteins. We show here that WRN functionally interacts with DNA polymerase δ (pol δ), a eukaryotic polymerase required for DNA replication and DNA repair. WRN increases the rate of nucleotide incorporation by pol δ in the absence of proliferating cell nuclear antigen (PCNA) but does not stimulate the activity of eukaryotic DNA polymerases α or ɛ, or a variety of other DNA polymerases. Moreover, we show that functional interaction with WRN is mediated through the third subunit of pol δ: i.e., Pol32p of Saccharomyces cerevisae , corresponding to the recently identified p66 subunit of human pol δ. Absence of the third subunit abrogates stimulation by WRN, and stimulation is restored by reconstituting the three-subunit enzyme. Our findings suggest that WRN may facilitate pol δ-mediated DNA replication and/or DNA repair and that disruption of WRN-pol δ interaction in WS cells may contribute to the previously observed S-phase defects and/or the unusual sensitivity to a limited number of DNA damaging agents.