Journal
SCIENCE
Volume 317, Issue 5837, Pages 513-516Publisher
AMER ASSOC ADVANCEMENT SCIENCE
DOI: 10.1126/science.1144130
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Funding
- Howard Hughes Medical Institute Funding Source: Medline
- NIGMS NIH HHS [R01-GM065367, R01 GM060620, R01-GM060620, R01 GM065367] Funding Source: Medline
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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.
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