Human PIF1 clears secondary DNA structures by coupled DNA unwinding and rewinding activities.

Human PIF1 primarily functions as a DNA translocase that clears secondary DNA structures by coupling unwinding with rapid rewinding, with only modest net unwinding observed.

• Why it matters: Understanding the biochemical activity of human PIF1 is crucial because it plays a key role in maintaining genome stability during DNA replication and repair, yet its precise mechanism has been unclear.
• What they did: The study compared full-length human PIF1 and yeast Pif1 using bulk assays and single-molecule magnetic tweezers, revealing that human PIF1’s apparent weak unwinding results from rapid reannealing rather than impaired motor activity, and that it efficiently remodels G-quadruplex DNA.
• The result: Findings suggest that human PIF1’s primary role is to resolve secondary DNA structures through coupled unwinding and rewinding, enabling genome stability without extensive single-stranded DNA formation.