Mechanism of asymmetric polymerase assembly at the eukaryotic replication fork

Nat Struct Mol Biol. 2014 Aug;21(8):664-70. doi: 10.1038/nsmb.2851. Epub 2014 Jul 6.


Eukaryotes use distinct polymerases for leading- and lagging-strand replication, but how they target their respective strands is uncertain. We reconstituted Saccharomyces cerevisiae replication forks and found that CMG helicase selects polymerase (Pol) ɛ to the exclusion of Pol δ on the leading strand. Even if Pol δ assembles on the leading strand, Pol ɛ rapidly replaces it. Pol δ-PCNA is distributive with CMG, in contrast to its high stability on primed ssDNA. Hence CMG will not stabilize Pol δ, instead leaving the leading strand accessible for Pol ɛ and stabilizing Pol ɛ. Comparison of Pol ɛ and Pol δ on a lagging-strand model DNA reveals the opposite. Pol δ dominates over excess Pol ɛ on PCNA-primed ssDNA. Thus, PCNA strongly favors Pol δ over Pol ɛ on the lagging strand, but CMG over-rides and flips this balance in favor of Pol ɛ on the leading strand.

Publication types

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

MeSH terms

  • DNA Polymerase II / chemistry*
  • DNA Polymerase III / chemistry*
  • DNA Replication*
  • DNA, Fungal / biosynthesis
  • DNA, Fungal / chemistry
  • DNA, Fungal / genetics
  • DNA-Binding Proteins / chemistry
  • Kinetics
  • Minichromosome Maintenance Proteins / chemistry
  • Nuclear Proteins / chemistry
  • Proliferating Cell Nuclear Antigen / chemistry
  • Replication Protein A / chemistry
  • Ribonucleoprotein, U4-U6 Small Nuclear / chemistry
  • Ribonucleoprotein, U5 Small Nuclear / chemistry
  • Saccharomyces cerevisiae / enzymology*
  • Saccharomyces cerevisiae / genetics
  • Saccharomyces cerevisiae Proteins / chemistry


  • CDC45 protein, S cerevisiae
  • DNA, Fungal
  • DNA-Binding Proteins
  • Nuclear Proteins
  • POL30 protein, S cerevisiae
  • PRP8 protein, S cerevisiae
  • Proliferating Cell Nuclear Antigen
  • Replication Protein A
  • Ribonucleoprotein, U4-U6 Small Nuclear
  • Ribonucleoprotein, U5 Small Nuclear
  • Saccharomyces cerevisiae Proteins
  • DNA Polymerase II
  • DNA Polymerase III
  • Minichromosome Maintenance Proteins