Details

Autor(en) / Beteiligte

• Fu, Yu V.
• Yardimci, Hasan
• Long, David T.
• Guainazzi, Angelo
• Bermudez, Vladimir P.
• Hurwitz, Jerard
• van Oijen, Antoine
• Schärer, Orlando D.
• Walter, Johannes C.

Titel

Selective Bypass of a Lagging Strand Roadblock by the Eukaryotic Replicative DNA Helicase

Ist Teil von

• Cell, 2011-09, Vol.146 (6), p.931-941

Ort / Verlag

United States: Elsevier Inc

Erscheinungsjahr

2011

Quelle

Access via ScienceDirect (Elsevier)

Beschreibungen/Notizen

• 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. [Display omitted] ► Replicative helicase CMG can bypass a lagging strand but not a leading strand roadblock ► This suggests that native CMG translocates along ssDNA in the 3′ to 5′ direction ► MCM2-7 reconfigures from a dsDNA to a ssDNA binding mode during replication initiation Replicative helicases are loaded onto double-stranded DNA. However, it is now clear that they translocate along single-stranded DNA to unwind the helix, suggesting a tricky topological transition takes place at replication origins.