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DNA polymerase III of Mycoplasma pulmonis: isolation and characterization of the enzyme and its structural gene, polC
Author(s) -
Barnes Marjorie H.,
Tarantino Paul M.,
Spacciapoli Peter,
Brown Neal C.,
Yu Huilan,
Dybvig Kevin
Publication year - 1994
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.1994.tb00476.x
Subject(s) - biology , dna polymerase , gene , isolation (microbiology) , polymerase , dna , enzyme , mycoplasma , genetics , microbiology and biotechnology , biochemistry
Summary 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 rigorousiy 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.