Functional uncoupling of twin polymerases: mechanism of polymerase dissociation from a lagging-strand block

J Biol Chem. 2004 May 14;279(20):21543-51. doi: 10.1074/jbc.M401649200. Epub 2004 Mar 9.

Abstract

Replication forks are constantly subjected to events that lead to fork stalling, stopping, or collapse. Using a synthetic rolling circle DNA substrate, we demonstrate that a block to the lagging-strand polymerase does not compromise helicase or leading-strand polymerase activity. In fact, lagging-strand synthesis also continues. Thus, the blocked lagging-strand enzyme quickly dissociates from the block site and resumes synthesis on new primed sites. Furthermore, studies in which the lagging polymerase is continuously blocked show that the leading polymerase continues unabated even as it remains attached to the lagging-strand enzyme. Hence, upon encounter of a block to the lagging stand, the polymerases functionally uncouple yet remain physically associated. Further study reveals that naked single-stranded DNA results in disruption of a stalled polymerase from its beta-DNA substrate. Thus, as the replisome advances, the single-stranded DNA loop that accumulates on the lagging-strand template releases the stalled lagging-strand polymerase from beta after SSB protein is depleted. The lagging-strand polymerase is then free to continue Okazaki fragment production.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • DNA / biosynthesis*
  • DNA Helicases / metabolism*
  • DNA Polymerase III / metabolism*
  • DNA Replication
  • DNA, Circular / biosynthesis
  • DNA, Circular / chemistry
  • DNA, Single-Stranded / biosynthesis
  • DNA, Single-Stranded / metabolism
  • Dimerization
  • Models, Molecular
  • Protein Conformation
  • Templates, Genetic

Substances

  • DNA, Circular
  • DNA, Single-Stranded
  • DNA
  • DNA Polymerase III
  • DNA Helicases