Journal
NATURE
Volume 492, Issue 7428, Pages 205-+Publisher
NATURE PUBLISHING GROUP
DOI: 10.1038/nature11730
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Funding
- National Institutes of Health (NIH) [GM62267, HL098316, GM077248, GM5 R01 GM034559, GM086466]
- American Cancer Society (ACS) [RSG0823401GMC]
- Netherlands Organization for Scientific Research (NWO) [Vici 680-47-607]
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Replicative DNA helicases generally unwind DNA as a single hexamer that encircles and translocates along one strand of the duplex while excluding the complementary strand (known as steric exclusion). By contrast, large T antigen, the replicative DNA helicase of the simian virus 40 (SV40), is reported to function as a pair of stacked hexamers that pumps double-stranded DNA through its central channel while laterally extruding single-stranded DNA. Here we use single-molecule and ensemble assays to show that large T antigen assembled on the SV40 origin unwinds DNA efficiently as a single hexamer that translocates on single-stranded DNA in the 3'-to-5' direction. Unexpectedly, large T antigen unwinds DNA past a DNA-protein crosslink on the translocation strand, suggesting that the large T antigen ring can open to bypass bulky adducts. Together, our data underscore the profound conservation among replicative helicase mechanisms, and reveal a new level of plasticity in the interactions of replicative helicases with DNA damage.
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