The mechanism of DNA unwinding by the eukaryotic replicative helicase

Nat Commun. 2019 May 14;10(1):2159. doi: 10.1038/s41467-019-09896-2.

Abstract

Accurate DNA replication is tightly regulated in eukaryotes to ensure genome stability during cell division and is performed by the multi-protein replisome. At the core an AAA+ hetero-hexameric complex, Mcm2-7, together with GINS and Cdc45 form the active replicative helicase Cdc45/Mcm2-7/GINS (CMG). It is not clear how this replicative ring helicase translocates on, and unwinds, DNA. We measure real-time dynamics of purified recombinant Drosophila melanogaster CMG unwinding DNA with single-molecule magnetic tweezers. Our data demonstrates that CMG exhibits a biased random walk, not the expected unidirectional motion. Through building a kinetic model we find CMG may enter up to three paused states rather than unwinding, and should these be prevented, in vivo fork rates would be recovered in vitro. We propose a mechanism in which CMG couples ATP hydrolysis to unwinding by acting as a lazy Brownian ratchet, thus providing quantitative understanding of the central process in eukaryotic DNA replication.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • DNA Helicases / isolation & purification
  • DNA Helicases / metabolism*
  • DNA Replication*
  • Drosophila Proteins / isolation & purification
  • Drosophila Proteins / metabolism*
  • Magnetic Phenomena
  • Models, Molecular*
  • Optical Tweezers
  • Recombinant Proteins / isolation & purification
  • Recombinant Proteins / metabolism
  • Single Molecule Imaging / methods

Substances

  • Drosophila Proteins
  • Recombinant Proteins
  • DNA Helicases