The molar ratio of σ73 to core polymerase in the obligate intracellular bacterium, Rickettsia prowazekii

Han‐Fei ‐F Ding, Herbert H. Winkler

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In the obligate Intracellular parasitic bacterium, Rickettsia prowazekii, the molar ratio of σ73 to core RNA polymerase, that is, the degree of saturation of the core polymerase by the catalytically active sigma factor, was very low. This ratio was determined from the radioactivity in rickettsial RNA polymerase immuno‐precipitated from crude extracts of infected L929 cells in which the parasite was exponentially growing. If we assume that, as Is true for the σ subunit, in R. prowazekii and Escherichia coli the β’and β subunits of the RNA polymerase have similar methionine and cysteine contents (the radiolabelled amino acids), the molar ratio of σ73 to core polymerase in R prowazekii would be 0.1. This is in striking contrast to E. Coli where the ratio is typically 0.4. it remains to be established whether this low sigma saturation results In a limitation of active RNA polymerase in R. prowazekii and contributes to its slow growth.

Original languageEnglish (US)
Pages (from-to)869-873
Number of pages5
JournalMolecular Microbiology
Issue number5
StatePublished - Mar 1994
Externally publishedYes


ASJC Scopus subject areas

  • Microbiology
  • Molecular Biology

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