Single-Molecule Studies Reveal Dynamics of DNA Unwinding by the Ring-Shaped T7 Helicase

Daniel S. Johnson, Lu Bai, Benjamin Y. Smith, Smita S. Patel, Michelle D. Wang

Research output: Contribution to journalArticlepeer-review

202 Scopus citations


Helicases are molecular motors that separate DNA strands for efficient replication of genomes. We probed the kinetics of individual ring-shaped T7 helicase molecules as they unwound double-stranded DNA (dsDNA) or translocated on single-stranded DNA (ssDNA). A distinctive DNA sequence dependence was observed in the unwinding rate that correlated with the local DNA unzipping energy landscape. The unwinding rate increased ∼10-fold (approaching the ssDNA translocation rate) when a destabilizing force on the DNA fork junction was increased from 5 to 11 pN. These observations reveal a fundamental difference between the mechanisms of ring-shaped and nonring-shaped helicases. The observed force-velocity and sequence dependence are not consistent with a simple passive unwinding model. However, an active unwinding model fully supports the data even though the helicase on its own does not unwind at its optimal rate. This work offers insights into possible ways helicase activity is enhanced by associated proteins.

Original languageEnglish (US)
Pages (from-to)1299-1309
Number of pages11
Issue number7
StatePublished - Jun 29 2007

All Science Journal Classification (ASJC) codes

  • General Biochemistry, Genetics and Molecular Biology


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