Real-time observation of bacteriophage T4 gp41 helicase reveals an unwinding mechanism

Timothée Lionnet, Michelle M. Spiering, Stephen J. Benkovic, David Bensimon, Vincent Croquette

Research output: Contribution to journalArticlepeer-review

125 Scopus citations


Helicases are enzymes that couple ATP hydrolysis to the unwinding of double-stranded (ds) nucleic acids. The bacteriophage T4 helicase (gp41) is a hexameric helicase that promotes DNA replication within a highly coordinated protein complex termed the replisome. Despite recent progress, the gp41 unwinding mechanism and regulatory interactions within the replisome remain unclear. Here we use a single tethered DNA hairpin as a real-time reporter of gp41-mediated dsDNA unwinding and single-stranded (ss) DNA translocation with 3-base pair (bp) resolution. Although gp41 translocates on ssDNA as fast as the in vivo replication fork (≈400 bp/s), its unwinding rate extrapolated to zero force is much slower (≈30 bp/s). Together, our results have two implications: first, gp41 unwinds DNA through a passive mechanism; second, this weak helicase cannot efficiently unwind the T4 genome alone. Our results suggest that important regulations occur within the replisome to achieve rapid and processive replication.

Original languageEnglish (US)
Pages (from-to)19790-19795
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number50
StatePublished - Dec 11 2007

All Science Journal Classification (ASJC) codes

  • General


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