DNA helicase-mediated packaging of adeno-associated virus type 2 genomes into preformed capsids

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Abstract
Helicases not only catalyse the disruption of hydrogen bonding between complementary regions of nucleic acids, but also move along nucleic acid strands in a polar fashion. Here we show that the Rep52 and Rep40 proteins of adeno‐associated virus type 2 (AAV‐2) are required to translocate capsid‐associated, single‐stranded DNA genomes into preformed empty AAV‐2 capsids, and that the DNA helicase function of Rep52/40 is essential for this process. Furthermore, DNase protection experiments suggest that insertion of AAV‐2 genomes proceeds from the 3′ end, which correlates with the 3′→5′ processivity demonstrated for the Rep52/40 helicase. A model is proposed in which capsid‐immobilized helicase complexes act as molecular motors to ‘pump’ single‐stranded DNA across the capsid boundary.