title: Selective bypass of a lagging strand roadblock by the eukaryotic replicative DNA helicase.
abstract: The eukaryotic replicative DNA helicase, CMG, unwinds DNA by an unknown mechanism. In some models, CMG encircles and translocates along one strand of DNA while excluding the other strand. In others, CMG encircles and translocates along duplex DNA. To distinguish between these models, replisomes were confronted with strand-specific DNA roadblocks in Xenopus egg extracts. An ssDNA translocase should stall at an obstruction on the translocation strand but not the excluded strand, whereas a dsDNA translocase should stall at obstructions on either strand. We found that replisomes bypass large roadblocks on the lagging strand template much more readily than on the leading strand template. Our results indicate that CMG is a 3' to 5' ssDNA translocase, consistent with unwinding via "steric exclusion." Given that MCM2-7 encircles dsDNA in G1, the data imply that formation of CMG in S phase involves remodeling of MCM2-7 from a dsDNA to a ssDNA binding mode.
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Yu V
authors.initials: YV
authors.lastname: Fu
authors.forename: Hasan
authors.initials: H
authors.lastname: Yardimci
authors.forename: David T
authors.initials: DT
authors.lastname: Long
authors.forename: The Vinh
authors.initials: TV
authors.lastname: Ho
authors.forename: Angelo
authors.initials: A
authors.lastname: Guainazzi
authors.forename: Vladimir P
authors.initials: VP
authors.lastname: Bermudez
authors.forename: Jerard
authors.initials: J
authors.lastname: Hurwitz
authors.forename: Antoine
authors.initials: A
authors.lastname: van Oijen
authors.forename: Orlando D
authors.initials: OD
authors.lastname: Schärer
authors.forename: Johannes C
authors.initials: JC
authors.lastname: Walter
mesh_terms: D000818:Animals; D004247:DNA / Q000378:metabolism*; D004265:DNA Helicases / Q000378:metabolism*; D004261:DNA Replication; D004277:DNA, Single-Stranded / Q000378:metabolism; D008954:Models, Biological; D016196:S Phase; D014981:Xenopus / Q000378:metabolism*
chemical_list: D004277:DNA, Single-Stranded; D004247:DNA; D004265:DNA Helicases