Revealing secrets of the enigmatic omega subunit of bacterial RNA polymerase

Juha Kurkela, Julia Fredman, Tiina A Salminen, Taina Tyystjärvi

Research output: Contribution to journalArticleScientificpeer-review

12 Citations (Scopus)


The conserved omega (ω) subunit of RNA polymerase (RNAP) is the only nonessential subunit of bacterial RNAP core. The small ω subunit (7 kDa-11.5 kDa) contains three conserved α helices, and helices α2 and α3 contain five fully conserved amino acids of ω. Four conserved amino acids stabilize the correct folding of the ω subunit and one is located in the vicinity of the β' subunit of RNAP. Otherwise ω shows high variation between bacterial taxa, and although the main interaction partner of ω is always β', many interactions are taxon-specific. ω-less strains show pleiotropic phenotypes, and based on in vivo and in vitro results, a few roles for the ω subunits have been described. Interactions of the ω subunit with the β' subunit are important for the RNAP core assembly and integrity. In addition, the ω subunit plays a role in promoter selection, as ω-less RNAP cores recruit fewer primary σ factors and more alternative σ factors than intact RNAP cores in many species. Furthermore, the promoter selection of an ω-less RNAP holoenzyme bearing the primary σ factor seems to differ from that of an intact RNAP holoenzyme.

Original languageEnglish
Pages (from-to)1-11
JournalMolecular Microbiology
Issue number1
Publication statusPublished - 2021
MoE publication typeA1 Journal article-refereed


  • gene regulation
  • recruitment of sigma factor
  • RNA polymerase
  • the omega subunit
  • transcription


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