Nucleic Acids Research Advance Access published online on July 25, 2008
Nucleic Acids Research, doi:10.1093/nar/gkn468
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Molecular Biology |
WRN Exonuclease activity is blocked by specific oxidatively induced base lesions positioned in either DNA strand
1Danish Centre for Molecular Gerontology, Department of Molecular Biology, University of Aarhus, Denmark, 2Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA, 3Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA, 4Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw and 5Institute of Genetics and Biotechnology, Warsaw University, Warsaw, Poland
*To whom correspondence should be addressed. Tel: +45 8942 2657; Fax: +45 8942 2650; Email: tvs{at}mb.au.dk
Received June 4, 2008. Revised July 3, 2008. Accepted July 3, 2008.
Werner syndrome (WS) is a premature aging disorder caused by mutations in the WS gene (WRN). Although WRN has been suggested to play an important role in DNA metabolic pathways, such as recombination, replication and repair, its precise role still remains to be determined. WRN possesses ATPase, helicase and exonuclease activities. Previous studies have shown that the WRN exonuclease is inhibited in vitro by certain lesions induced by oxidative stress and positioned in the digested strand of the substrate. The presence of the 70/86 Ku heterodimer (Ku), participating in the repair of double-strand breaks (DSBs), alleviates WRN exonuclease blockage imposed by the oxidatively induced DNA lesions. The current study demonstrates that WRN exonuclease is inhibited by several additional oxidized bases, and that Ku stimulates the WRN exonuclease to bypass these lesions. Specific lesions present in the non-digested strand were shown also to inhibit the progression of the WRN exonuclease; however, Ku was not able to stimulate WRN exonuclease to bypass these lesions. Thus, this study considerably broadens the spectrum of lesions which block WRN exonuclease progression, shows a blocking effect of lesions in the non-digested strand, and supports a function for WRN and Ku in a DNA damage processing pathway.
Present addresses: Zuzanna Bukowy, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland
Jeanine A Harrigan, The WellcomeTrust/CRUK Gurdon Institute, University of Cambridge, Tennis Court Road, Cambridge, England