The RNA polymerases of Porphyromonas gingivalis and Fusobacterium nucleatum are unrelated to the RNA polymerase of Escherichia coli.

Western blot analysis that used antisera to the E. coli core enzyme and sigma factors was used for examination of the RNA polymerase of Actinobacillus actinomycetemcomitans, Streptococcus mutans, Fusobacterium nucleatum, and Porphyromonas gingivalis. Both antisera reacted with proteins in A. actinomycetemcomitans and S. mutans whole-cell extracts. Reactions were seen with some F. nucleatum proteins when the anti-core RNA polymerase antisera were used, but the cross-reacting proteins were not of an expected molecular weight for beta or beta'. No reaction with F. nucleatum proteins was seen when extracts were reacted with antisera to E. coli sigma factor. There were no cross-reacting proteins detected in P. gingivalis extracts with either antisera. These results suggest that E. coli RNA polymerase may not be sufficiently similar to P. gingivalis and F. nucleatum RNA polymerase for E. coli RNA polymerase to recognize P. gingivalis or F. nucleatum promoters. Partially purified P. gingivalis and F. nucleatum RNA polymerase exhibited a specificity for a P. gingivalis DNA template, while having a decreased activity from an E. coli DNA template. The antibiotic sensitivity profile of P. gingivalis and F. nucleatum RNA polymerase activity was shown to differ from that of E. coli, with these activities not being affected by rifampicin, streptovaricin, or streptolydigin. We conclude that the efficient cloning and expression of P. gingivalis and F. nucleatum genes in E. coli will require the use of promoter-containing expression vectors.