||Bacteria Escherichia coli
||Ishihama A, Functional modulation of Escherichia coli RNA polymerase. Annu Rev Microbiol. 2000 54: 499-518. DOI: 10.1146/annurev.micro.54.1.499 p.501 2nd paragraphPubMed ID11018136
|| Jishage M, Ishihama A. 1995. Regulation of RNA polymerase sigma subunit synthesis in Escherichia coli: intracellular levels of σ70 and σ38. J. Bacteriol. 177: 6832–35  Jishage M, Iwata A, Ueda S, Ishihama A. 1996. Regulation of RNA polymerase sigma subunit synthesis in Escherichia coli: intracellular levels of four species of sigma subunit under various growth conditions. J. Bacteriol. 178: 5447–51PubMed ID7592475, 8808934
||P.501 2nd paragraph: "Because RNA chain elongation is catalyzed by core enzyme without an associated σ subunit, the combined number (1200 molecules) of all seven σ subunits (primary sources) is more than the total number (600–700 molecules) of core enzyme molecules that are not involved in transcription and thus are available for binding σ (Figure 2, see color insert). The majority of free RNA polymerase molecules in the cytosol should therefore be in the holoenzyme form, associated with one of the σ subunits. These findings support the model that competition takes place between the σ subunits for binding a limited supply of core enzyme. To estimate the relative levels of different holoenzyme forms, two parameters must be determined: the intracellular concentrations of all seven σ subunits and the binding affinity of core enzyme to each σ subunit."