Assembly of a chromosomal replication machine: two DNA polymerases, a clamp loader, and sliding clamps in one holoenzyme particle. III. Interface between two polymerases and the clamp loader

J Biol Chem. 1995 Jun 2;270(22):13366-77. doi: 10.1074/jbc.270.22.13366.


The nine-subunit DNA polymerase (Pol) III* coupled to its beta sliding clamp is a rapid and highly processive replicating machine. The multiple subunits are needed for the complicated task of duplicating the Escherichia coli chromosome. In this report, Pol III* was constituted from individual pure proteins, and its structure was studied. Constitution of the Pol III* particle requires an ordered addition of the subunits, and the final structure contains 14 polypeptides in the ratio alpha 2 epsilon 2 theta 2 tau 2 gamma 2 delta 1 delta' 1 chi 1 psi 1. The structure can be summarized as being composed of two core polymerases (alpha epsilon theta) held together by a dimer of tau and one gamma complex clamp loader (gamma 2 delta 1 delta' 1 chi 1 psi 1) for loading beta onto DNA. At the center of the structure, the related tau and gamma subunits form a heterotetramer upon which the two core polymerases and clamp loader proteins assemble. The single copy nature of the delta, delta', chi, and psi subunits confers a structural asymmetry with respect to the two polymerases, presumably for the different functions of replicating the leading and lagging strands.

Publication types

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

MeSH terms

  • Chromosomes, Bacterial*
  • DNA Polymerase III / chemistry
  • DNA Polymerase III / metabolism*
  • DNA Replication*
  • DNA-Directed DNA Polymerase / chemistry
  • DNA-Directed DNA Polymerase / metabolism
  • Escherichia coli / genetics
  • Isoenzymes / chemistry
  • Isoenzymes / metabolism*
  • Protein Binding
  • Protein Conformation


  • Isoenzymes
  • DNA replicase
  • DNA Polymerase III
  • DNA-Directed DNA Polymerase