MOLECULAR BIOLOGY: Prospective Sampling

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Science  07 Sep 2007:
Vol. 317, Issue 5843, pp. 1295d
DOI: 10.1126/science.317.5843.1295d

Like its chemical cousin DNA, the most common structural motif adopted by RNA is the double helix. There are many instances (transcription, pre-mRNA processing, and ribosome biogenesis) where double-stranded RNA (dsRNA) needs to be unwound and unzipped, functions performed by motor proteins known as RNA helicases. To understand more about how helicases go about their business, Cheng et al. have challenged the hepatitis C virus NS3 helicase with strong-versus- weak and long-versus-short barriers. They show that NS3 readily unzips a hairpin of 30 A:U base pairs but dissociates or pauses before entering the same length of more stable G:C base pairs. When faced with a three-G:C base pair zipper, NS3 ploughs right on through, yet lengthening the barrier to six G:C base pairs causes NS3 to pause, indicating that the enzyme must be sampling the RNA just ahead of where helicase-mediated unwinding takes place. The former interaction may serve to destabilize the dsRNA during the pause that precedes unwinding and thereby enhance the processivity of the enzyme. — GR

Proc. Natl. Acad. Sci. U.S.A. 104, 13954 (2007).

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