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A sigma factor is the promoter specificity subunit of eubacterial-type multisubunit RNA polymerases, those whose core subunit composition is often described as alpha(2)-beta-beta-prime. (This type of multisubunit RNA polymerase complex is known to be found in eubacteria and plant plastids). Although sigma does not bind DNA on its own, when combined with the core to form the holoenzyme, this binds specifically to promoter sequences, with the sigma factor making sequence specific contacts with the promoter elements. The sigma subunit is released from the elongating form of the polymerase and is thus free to act catalytically for multiple RNA polymerase core enzymes. A transcription factor activity that confers promoter specificity upon mitochondrial RNA polymerase, in a manner analogous to eubacterial sigma factors. Elemental activities, such as catalysis or binding, describing the actions of a gene product at the molecular level. A given gene product may exhibit one or more molecular functions. null Plays a role in regulating transcription; may bind a promoter or enhancer DNA sequence or interact with a DNA-binding transcription factor.

View Gene Ontology (GO) Term


Name: transcription initiation factor activity
Acc: GO:0016986
Aspect: Molecular Function
  • transcriptional initiation factor activity
Proteins in PDR annotated with:
   This term: 53 [Search]
   Term or descendants: 165 [Search]


GO:0016986 - transcription initiation factor activity (interactive image map)

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