Spring-loaded mechanism of DNA unwinding by hepatitis C virus NS3 helicase

Sua Myong, Michael M. Bruno, Anna M. Pyle, Taekjip Ha

Research output: Contribution to journalArticlepeer-review


NS3, an essential helicase for replication of hepatitis C virus, is a model enzyme for investigating helicase function. Using single-molecule fluorescence analysis, we showed that NS3 unwinds DNA in discrete steps of about three base pairs (bp). Dwell time analysis indicated that about three hidden steps are required before a 3-bp step is taken. Taking into account the available structural data, we propose a spring-loaded mechanism in which several steps of one nucleotide per adenosine triphosphate molecule accumulate tension on the protein-DNA complex, which is relieved periodically via a burst of 3-bp unwinding. NS3 appears to shelter the displaced strand during unwinding, and, upon encountering a barrier or after unwinding >18 bp, it snaps or slips backward rapidly and repeats unwinding many times in succession. Such repetitive unwinding behavior over a short stretch of duplex may help to keep secondary structures resolved during viral genome replication.

Original languageEnglish (US)
Pages (from-to)513-516
Number of pages4
Issue number5837
StatePublished - Jul 27 2007

ASJC Scopus subject areas

  • General


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