DNA Polymerase III of Escherichia coli

DNA polymerase III, the core of the DNA polymerase III holoenzyme, has been purified Z&000-fold to 97% homogeneity from Escherichiu coli HMS-83. The enzyme contains three subunits: (Y, E, and 0 of 140,000, 25,000, and 10,000 daltons, respectively. The cy subunit has been previously shown to be a component of both DNA polymerase III and the more complex DNA polymerase III holoenzyme (Livingston, D. M., Hinkle, D., and Richardson, C. (1975) J. Biol. Chem. 250, 461-469; McHenry, C., and Kornberg, A. (1977) J. Biol. Chem. 252,6478-6484). It is demonstrated here that the E and B subunits are also subunits of the DNA polymerase III holoenzyme. Thus, the DNA polymerase III holoenzyme contains at least six different subunits. Our preparation has both the 3’ + 5’ and 5’ + 3’ exonuclease activities previously assigned to DNA polymerase III (Livingston, D., and Richardson, C. (1975) J. Biol. Chem. 250, 470478).