Nuclear DNA polymerases and the HeLa cell cycle

J Biol Chem. 1975 Oct 10;250(19):7951-7.


Purified nuclei of HeLa S3 cells contain two DNA-dependent DNA polymerases that have distinct physical and enzymatic properties. We have investigated the variations in their activity during the cell cycle of a synchronized culture. Cells were synchronized by a double thymidine block, harvested at various phases of the cycle, and the two DNA polymerases were purified partially by DEAE-cellulose and phosphocellulose chromatography. The activity of DNA polymerase I (low molecular weight, N-ethylmaleimide-insensitive) remains essentially constant throughout the cycle. The activity of DNA polymerase II (high molecular weight, N-ethylmaleimide-sensitive), however, increases during G1 to mid-S and declines, 7- to 10-fold between late-S and G2. Addition of cycloheximide (60 mug/ml) to cultures 12 hours after the release from thymidine block abolishes the rise in the activity of DNA polymerase II. Cycloheximide also reduced the activity of DNA polymerase I by 60%. Addition of hydroxyurea (1mM) at 1 hour after release has no effect on the activity of either enzyme. We conclude that in HeLa cells, DNA polymerase I and II are distinct enzymes, that DNA polymerase II probably functions in DNA replication and is probably induced in response to stimuli for DNA biosynthesis.

Publication types

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

MeSH terms

  • Cell Division / drug effects
  • Cell Nucleus / drug effects
  • Cell Nucleus / enzymology*
  • Cell Nucleus / ultrastructure
  • Cycloheximide / pharmacology
  • DNA Nucleotidyltransferases / isolation & purification
  • DNA Nucleotidyltransferases / metabolism*
  • Ethylmaleimide / pharmacology
  • HeLa Cells / enzymology*
  • Hydrogen-Ion Concentration
  • Hydroxyurea / pharmacology
  • Isoenzymes / isolation & purification
  • Isoenzymes / metabolism*
  • Kinetics
  • Magnesium / pharmacology
  • Microscopy, Electron
  • Templates, Genetic


  • Isoenzymes
  • Cycloheximide
  • DNA Nucleotidyltransferases
  • Magnesium
  • Ethylmaleimide
  • Hydroxyurea