PcrA helicase dismantles RecA filaments by reeling in DNA in uniform steps

Jeehae Park, Sua Myong, Anita Niedziela-Majka, Kyung Suk Lee, Jin Yu, Timothy M. Lohman, Taekjip Ha

Research output: Contribution to journalArticlepeer-review


Translocation of helicase-like proteins on nucleic acids underlies key cellular functions. However, it is still unclear how translocation can drive removal of DNA-bound proteins, and basic properties like the elementary step size remain controversial. Using single-molecule fluorescence analysis on a prototypical superfamily 1 helicase, Bacillus stearothermophilus PcrA, we discovered that PcrA preferentially translocates on the DNA lagging strand instead of unwinding the template duplex. PcrA anchors itself to the template duplex using the 2B subdomain and reels in the lagging strand, extruding a single-stranded loop. Static disorder limited previous ensemble studies of a PcrA stepping mechanism. Here, highly repetitive looping revealed that PcrA translocates in uniform steps of 1 nt. This reeling-in activity requires the open conformation of PcrA and can rapidly dismantle a preformed RecA filament even at low PcrA concentrations, suggesting a mode of action for eliminating potentially deleterious recombination intermediates.

Original languageEnglish (US)
Pages (from-to)544-555
Number of pages12
Issue number4
StatePublished - Aug 2010
Externally publishedYes


  • DNA

ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)


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