The Werner Syndrome Helicase Coordinates Sequential Strand Displacement and FEN1-Mediated Flap Cleavage during Polymerase δ Elongation

ABSTRACT

The Werner syndrome protein (WRN) suppresses the loss of telomeres replicated by lagging-strand synthesis by a yet to be defined mechanism. Here, we show that whereas either WRN or the Bloom syndrome helicase (BLM) stimulates DNA polymerase δ progression across telomeric G-rich repeats, only WRN promotes sequential strand displacement synthesis and FEN1 cleavage, a critical step in Okazaki fragment maturation, at these sequences. Helicase activity, as well as the conserved winged-helix (WH) motif and the helicase and RNase D C-terminal (HRDC) domain play important but distinct roles in this process. Remarkably, WRN also influences the formation of FEN1 cleavage products during strand displacement on a nontelomeric substrate, suggesting that WRN recruitment and cooperative interaction with FEN1 during lagging-strand synthesis may serve to regulate sequential strand displacement and flap cleavage at other genomic sites. These findings define a biochemical context for the physiological role of WRN in maintaining genetic stability.

KEYWORDS:

• Werner syndrome
• telomeres
• DNA replication
• lagging-strand synthesis
• DNA helicase
• Okazaki fragment
• aging
• lagging strand

Supplemental material for this article may be found at https://doi.org/10.1128/MCB.00560-16.

ACKNOWLEDGMENTS

We thank Michael Lieber for FEN1 cDNA and members of the Comai laboratory for suggestions and valuable discussions.

This work was supported by a grant from the National Institutes of Health (R01AG034156 to L.C.) and was conducted in a facility constructed with support from Research Facilities Improvement Program grants C06 RR014514-01, C06 RR10600-01, and C06 CA62528 from the National Center for Research Resources, National Institutes of Health.

B.L. designed, performed, and analyzed all the experiments described and contributed to the preparation of the manuscript. S.R. contributed to the design of the study and the interpretation of data. L.C. conceived and coordinated the study and wrote the paper, together with B.L. We all analyzed the results and approved the final version of the manuscript.