OBO ID: GO:0016987

Term Name:	sigma factor activity		Search Ontology:
Synonyms:	bacterial sigma factor activity core DNA-dependent RNA polymerase binding promoter specificity activity DNA-dependent RNA polymerase promoter selection factor plastid sigma factor activity promoter selection factor activity sigma transcription factor
Definition:	Sigma factors act as the promoter specificity subunit of eubacterial and plant plastid multisubunit RNA polymerases, whose core subunit composition is often described as alpha(2)-beta-beta-prime. Although sigma does not bind DNA on its own, when combined with the core to form the holoenzyme, the sigma factor binds specifically to promoter elements. The sigma subunit is released once elongation begins.
References:
Ontology:	GO: Molecular Function    QuickGO    AmiGO