||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.500 top paragraph & p.501 2nd paragraphPubMed ID11018136
|| Ishihama A. 1981. Subunit assembly of Escherichia coli RNA polymerase. Adv. Biophys. 14: 1–35  Ishihama A, Taketo M, Saitoh T, Fukuda R. 1976. Control of formation of RNA polymerase in Escherichia coli. In RNA Polymerase, ed. M Camberlin, R Losick, pp. 475–502. Cold Spring Harbor, NY: Cold Spring Harbor Lab. PressPubMed ID7015808
||P.499 bottom paragraph: "The RNA polymerase of Escherichia coli is composed of the core enzyme (subunit composition, α2ββ') with the catalytic activity of RNA polymerization, and one of the seven different species of σ subunit, each responsible for recognition of a specific set of promoters (refs 28, 29, 31, 40). The total number of core enzyme molecules in a growing E. coli cell is ∼2000 (primary sources), which is less than the total number of genes (∼4000) on the E. coli genome (ref 7)." P.501 2nd paragraph: "The intracellular concentration of RNA polymerase in the steady state of growing E. coli W3350 cells is maintained at a constant level that is characteristic of the rate of cell growth (primary sources). In a rich medium, the total number of core enzyme molecules is ~2000 per genome equivalent of DNA, among which about one third are disengaged from the DNA."