DNA polymerase III of Mycoplasma pulmonis: isolation and characterization of the enzyme and its structural gene, polC

Mol Microbiol. 1994 Sep;13(5):843-54. doi: 10.1111/j.1365-2958.1994.tb00476.x.


Mycoplasmas have originated from Gram-positive bacteria via rapid degenerative evolution. The results of previous investigations of mycoplasmal DNA polymerases suggest that the process of evolution has wrought a major simplification of the typical Gram-positive bacterial DNA polymerase profile, reducing it from three exonuclease (exo)-positive enzymes to a single exo-negative species. The objective of this work was to rigorously investigate this suggestion, focusing on the evolutionary fate of DNA polymerase III (Pol III), the enzyme which Gram-positive bacteria specifically require for replicative DNA synthesis. The approach used Mycoplasma pulmonis as the model organism and exploited structural gene cloning, enzymology, and Pol III-specific inhibitors of the HPUra class as investigative tools. Our results indicate that M. pulmonis has strongly conserved a single copy of a structural gene homologous to polC, the Gram-positive bacterial gene encoding Pol III. M. pulmonis was found to possess a DNA polymerase that displays the size, primary structure, exonuclease activity, and level of HPUra sensitivity expected of a prototypical Gram-positive Pol III. The high level of sensitivity of M. pulmonis growth to Gram-positive Pol III-selective inhibitors of the HPUra type strongly suggests that Mycoplasma has conserved not only the basic structure of Pol III, but also its essential replicative function. Evidence for a second, HPUra-resistant polymerase activity in M. pulmonis is also described, indicating that the DNA polymerase composition of Mycoplasma is complex and closer to that of Gram-positive bacteria than previously thought.

Publication types

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

MeSH terms

  • Amino Acid Sequence
  • Antimetabolites / pharmacology
  • Bacillus subtilis / genetics
  • Bacterial Proteins / antagonists & inhibitors
  • Bacterial Proteins / genetics
  • Bacterial Proteins / isolation & purification*
  • Base Sequence
  • Cloning, Molecular
  • DNA Polymerase III / antagonists & inhibitors
  • DNA Polymerase III / genetics
  • DNA Polymerase III / isolation & purification*
  • DNA, Bacterial / genetics
  • Genes, Bacterial*
  • Molecular Sequence Data
  • Mycoplasma / enzymology*
  • Mycoplasma / genetics
  • Sequence Alignment
  • Sequence Homology, Amino Acid
  • Species Specificity
  • Uracil / analogs & derivatives
  • Uracil / pharmacology


  • Antimetabolites
  • Bacterial Proteins
  • DNA, Bacterial
  • 6-(4-hydroxyphenylhydrazino)uracil
  • Uracil
  • DNA Polymerase III

Associated data

  • GENBANK/P13267
  • GENBANK/U06833