The dimer of the beta subunit of Escherichia coli DNA polymerase III holoenzyme is dissociated into monomers upon binding magnesium(II). Journal Article uri icon



  • The beta subunit of Escherichia coli DNA polymerase III holoenzyme binds Mg2+. Reacting beta with fluoresceinmaleimide (FM) resulted in one label per beta monomer with full retention of activity. Titration of FM-beta with Mg2+ resulted in a saturable 11% fluorescence enhancement. Analysis indicated that there was one noncooperative magnesium binding site per beta monomer with a dissociation constant of 1.7 mM. Saturable fluorescence enhancement was also observed when titration was with Ca2+ or spermidine(3+) but not with the monovalent cations Na+ and K+. The Mg2+-induced fluorescence enhancement was specific for FM-beta and was not observed with FM-glutathione, dimethoxystilbenemaleimide-beta, or pyrenylmaleimide-beta. Gel filtration studies indicated that the beta dimer-monomer dissociation occurred at physiologically significant beta concentrations and that the presence of 10 mM Mg2+ shifted the dimer-monomer equilibrium to favor monomers. Both the gel-filtered dimers and the gel-filtered monomers were active in the replication assay. These and other results suggested that the fluorescence increase which accompanies beta dissociation is due to a relief from homoquenching of FM when the beta dimer dissociates into monomers.

publication date

  • July 12, 1988

has restriction

  • closed

Date in CU Experts

  • October 1, 2013 12:09 PM

Full Author List

  • Griep MA; McHenry CS

author count

  • 2

Other Profiles

International Standard Serial Number (ISSN)

  • 0006-2960

Additional Document Info

start page

  • 5210

end page

  • 5215


  • 27


  • 14