The structure of ORC-Cdc6 on an origin DNA reveals the mechanism of ORC activation by the replication initiator Cdc6

Nat Commun. 2021 Jun 23;12(1):3883. doi: 10.1038/s41467-021-24199-1.


The Origin Recognition Complex (ORC) binds to sites in chromosomes to specify the location of origins of DNA replication. The S. cerevisiae ORC binds to specific DNA sequences throughout the cell cycle but becomes active only when it binds to the replication initiator Cdc6. It has been unclear at the molecular level how Cdc6 activates ORC, converting it to an active recruiter of the Mcm2-7 hexamer, the core of the replicative helicase. Here we report the cryo-EM structure at 3.3 Å resolution of the yeast ORC-Cdc6 bound to an 85-bp ARS1 origin DNA. The structure reveals that Cdc6 contributes to origin DNA recognition via its winged helix domain (WHD) and its initiator-specific motif. Cdc6 binding rearranges a short α-helix in the Orc1 AAA+ domain and the Orc2 WHD, leading to the activation of the Cdc6 ATPase and the formation of the three sites for the recruitment of Mcm2-7, none of which are present in ORC alone. The results illuminate the molecular mechanism of a critical biochemical step in the licensing of eukaryotic replication origins.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Base Sequence
  • Cell Cycle Proteins / chemistry
  • Cell Cycle Proteins / genetics*
  • Cell Cycle Proteins / metabolism
  • Cryoelectron Microscopy
  • DNA Replication / genetics*
  • DNA, Fungal / chemistry
  • DNA, Fungal / genetics*
  • DNA, Fungal / metabolism
  • DNA-Binding Proteins / chemistry
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism
  • Models, Molecular
  • Nucleic Acid Conformation
  • Origin Recognition Complex / chemistry
  • Origin Recognition Complex / genetics*
  • Origin Recognition Complex / metabolism
  • Protein Binding
  • Protein Domains
  • Replication Origin / genetics*
  • Saccharomyces cerevisiae / genetics*
  • Saccharomyces cerevisiae / metabolism
  • Saccharomyces cerevisiae / ultrastructure
  • Saccharomyces cerevisiae Proteins / chemistry
  • Saccharomyces cerevisiae Proteins / genetics*
  • Saccharomyces cerevisiae Proteins / metabolism
  • Sequence Homology, Amino Acid
  • Sequence Homology, Nucleic Acid
  • Transcription Factors / chemistry
  • Transcription Factors / genetics
  • Transcription Factors / metabolism


  • ABFI protein, S cerevisiae
  • CDC6 protein, S cerevisiae
  • Cell Cycle Proteins
  • DNA, Fungal
  • DNA-Binding Proteins
  • Origin Recognition Complex
  • Saccharomyces cerevisiae Proteins
  • Transcription Factors