Beta*, a UV-inducible shorter form of the beta subunit of DNA polymerase III of Escherichia coli. II. Overproduction, purification, and activity as a polymerase processivity clamp

J Biol Chem. 1996 Feb 2;271(5):2491-6. doi: 10.1074/jbc.271.5.2491.


Control elements located inside the coding sequence of dnaN, the gene encoding the beta subunit of DNA polymerase III holoenzyme, direct the synthesis of a shorter and UV-inducible form of the beta subunit (Skaliter, R., Paz-Elizur, T., and Livneh, Z. (1996) J. Biol. Chem. 271, 2278-2281, and Paz-Elizur, T., Skaliter, R., Blumenstein, S., and Livneh, Z. (1996) J. Biol. Chem. 271, 2282-2290). The protein, termed beta*, was overproduced using the phage T7 expression system, leading to its accumulation as inclusion bodies at 5-10% of the total cellular proteins. beta* was purified in denatured form, followed by refolding to yield a preparation > 95% pure. Denatured beta* had a molecular mass of 26 kDa and contained two isoforms when analyzed by two-dimensional gel electrophoresis. The major isoform had a pI of 5.45, and comigrated with cellular beta*. Size exclusion high performance liquid chromatography under nondenaturing conditions and chemical cross-linking experiments indicate that beta* is a homotrimer. DNA synthesis by DNA polymerase III* was stimulated up to 10-fold by beta*, primarily due to an increase in the processivity of polymerization. It is suggested that beta* functions as an alternative sliding DNA clamp in a process associated with DNA synthesis in UV-irradiated cells.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphate / metabolism
  • Base Sequence
  • Blotting, Western
  • Chromatography, Gel
  • DNA Polymerase III / biosynthesis*
  • DNA Polymerase III / genetics
  • DNA Polymerase III / isolation & purification
  • DNA Polymerase III / metabolism
  • DNA Primers
  • Electrophoresis, Gel, Two-Dimensional
  • Enzyme Induction
  • Escherichia coli / enzymology
  • Escherichia coli / radiation effects*
  • Molecular Sequence Data
  • Molecular Weight
  • Protein Processing, Post-Translational
  • Ultraviolet Rays*


  • DNA Primers
  • Adenosine Triphosphate
  • DNA Polymerase III