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Updated: Aug 13, 2026

Single-Molecule Real-Time Visualization of DNA Unwinding by CMG Helicase
Published on: September 27, 2024
Dda helicase unwinds a DNA-PNA chimeric substrate: evidence for an inchworm mechanism
Travis L Spurling1, Robert L Eoff, Kevin D Raney
1Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA.
Abstract:
Helicases are ubiquitous enzymes involved in all aspects of DNA metabolism including replication, repair, recombination, and transcription. The mechanism of the bacteriophage T4 Dda helicase was investigated by preparing a DNA-PNA chimeric substrate. Surprisingly, Dda was able to unwind a substrate containing 12 PNA moieties in the loading strand of the enzyme. We suggest a mechanism whereby the Dda helicase contains two distinct DNA binding domains which allow an inchworm mechanism for translocation. A single step of the enzyme is sufficient to unwind the DNA-PNA chimera because several base pairs melt spontaneously due to thermal fraying. Hence, Dda helicase can unwind the substrate without actually translocating along the PNA.
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