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Published October 11, 2013 | Published
Journal Article Open

Dna2 Is Involved in CA Strand Resection and Nascent Lagging Strand Completion at Native Yeast Telomeres


Post-replicational telomere end processing involves both extension by telomerase and resection to produce 3′-GT-overhangs that extend beyond the complementary 5′-CA-rich strand. Resection must be carefully controlled to maintain telomere length. At short de novo telomeres generated artificially by HO endonuclease in the G_2 phase, we show that dna2-defective strains are impaired in both telomere elongation and sequential 5′-CA resection. At native telomeres in dna2 mutants, GT-overhangs do clearly elongate during late S phase but are shorter than in wild type, suggesting a role for Dna2 in 5′-CA resection but also indicating significant redundancy with other nucleases. Surprisingly, elimination of Mre11 nuclease or Exo1, which are complementary to Dna2 in resection of internal double strand breaks, does not lead to further shortening of GT-overhangs in dna2 mutants. A second step in end processing involves filling in of the CA-strand to maintain appropriate telomere length. We show that Dna2 is required for normal telomeric CA-strand fill-in. Yeast dna2 mutants, like mutants in DNA ligase 1 (cdc9), accumulate low molecular weight, nascent lagging strand DNA replication intermediates at telomeres. Based on this and other results, we propose that FEN1 is not sufficient and that either Dna2 or Exo1 is required to supplement FEN1 in maturing lagging strands at telomeres. Telomeres may be among the subset of genomic locations where Dna2 helicase/nuclease is essential for the two-nuclease pathway of primer processing on lagging strands.

Additional Information

© 2013 by The American Society for Biochemistry and Molecular Biology, Inc. Received for publication, March 26, 2013, and in revised form, August 19, 2013 Published, JBC Papers in Press, August 20, 2013. This work was supported, in whole or in part, by National Institutes of Health Grant GM078666. This work was also supported by Ellison Foundation Grant AG-SS-2143-08. We thank Robert Bambara and Lata Balakrishnan for interesting discussion; David Lydall and Greg Ngo for comments on the manuscript; Piotr Polaczek for preparation of figures; and Dan Gottschling, Charles Boone, and Svetlana Makovets for strains.

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Published - J._Biol._Chem.-2013-Budd-29414-29.pdf


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