The DnaX-binding subunits delta' and psi are bound to gamma and not tau in the DNA polymerase III holoenzyme

J Biol Chem. 2000 Feb 4;275(5):3017-20. doi: 10.1074/jbc.275.5.3017.


The DnaX complex subassembly of the DNA polymerase III holoenzyme is comprised of the DnaX proteins tau and gamma and the auxiliary subunits delta, delta', chi, and psi, which together load the beta processivity factor onto primed DNA in an ATP-dependent reaction. delta' and psi bind directly to DnaX whereas delta and chi bind to delta' and psi, respectively (Onrust, R., Finkelstein, J., Naktinis, V., Turner, J., Fang, L., and O'Donnell, M. (1995) J. Biol. Chem. 270, 13348-13357). Until now, it has been unclear which DnaX protein, tau or gamma, in holoenzyme binds the auxiliary subunits delta, delta', chi,and psi. Treatment of purified holoenzyme with the homobifunctional cross-linker bis(sulfosuccinimidyl)suberate produces covalently cross-linked gamma-delta' and gamma-psi complexes identified by Western blot analysis. Immunodetection of cross-linked species with anti-delta' and anti-psi antibodies revealed that no tau-delta' or tau-psi cross-links had formed, suggesting that the delta' and psi subunits reside only on gamma within holoenzyme.

Publication types

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

MeSH terms

  • Animals
  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / metabolism
  • Cross-Linking Reagents / chemistry
  • Cross-Linking Reagents / metabolism
  • DNA Polymerase III / chemistry*
  • DNA Polymerase III / metabolism
  • Escherichia coli / chemistry
  • Escherichia coli / metabolism
  • Holoenzymes / chemistry
  • Holoenzymes / metabolism


  • Bacterial Proteins
  • Cross-Linking Reagents
  • DnaX protein, Bacteria
  • Holoenzymes
  • DNA Polymerase III