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 ␦ 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.

Research on Werner Syndrome: Trends from Past to Present and Future Prospects

“…It has been suggested that WRN helicase supports the synthesis of the nascent lagging strand by replicative DNA polymerase while resolving the quadruplex structure [ 38 ]. In support of this, WRN helicase has been observed to stimulate DNA polymerase δ to proceed with DNA synthesis by overcoming G-rich repeats, and to promote the maturation of the Okazaki fragment in vitro [ 39 ] ( Figure 1 d).…”

Congenital Diseases of DNA Replication: Clinical Phenotypes and Molecular Mechanisms

“…Pol δ interacts with the Werner helicase and Werner syndrome shares many characteristics with MPD, including a bird-like face, loss of adipose tissue, joint contractures, scleroderma, hypogonadism and insulin resistance [ 101 , 105 ]. Werner helicase enhances pol δ activity, particularly at difficult-to-replicate secondary structures within common fragile sites, providing a rationale for the overlapping clinical phenotypes [ 181 , 182 , 183 ].…”

RecQ and Fe–S helicases have unique roles in DNA metabolism dictated by their unwinding directionality, substrate specificity, and protein interactions

“…A prominent partner of WRN is FEN-1 that cleaves 5′ flaps during BER and lagging strand DNA synthesis [10,173] (Figure 2). WRN co-ordinately stimulates pol δ strand displacement synthesis and FEN-1 cleavage of 5′ flaps [174] (Figure 3). Like WRN, FEN-1 deficiency diminishes lagging strand telomeric DNA replication; moreover, expression of a FEN-1 mutant defective in its interaction with WRN and shelterin protein TRF2 failed to rescue the telomere defect [175].…”