PMID:23201686

Citation	Yardimci, H, Wang, X, Loveland, AB, Tappin, I, Rudner, DZ, Hurwitz, J, van Oijen, AM and Walter, JC (2012) Bypass of a protein barrier by a replicative DNA helicase. Nature 492:205-9
Abstract	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.
Links	PubMed PMC3521859 Online version:10.1038/nature11730
Keywords	Antigens, Viral, Tumor/metabolism; DNA Helicases/metabolism; DNA Replication; DNA, Single-Stranded/metabolism; DNA, Viral/metabolism; Replication Origin/physiology; Simian virus 40/enzymology; Viral Proteins/metabolism
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