title: The actinobacterial transcription factor RbpA binds to the principal sigma subunit of RNA polymerase.
abstract: RbpA is a small non-DNA-binding transcription factor that associates with RNA polymerase holoenzyme and stimulates transcription in actinobacteria, including Streptomyces coelicolor and Mycobacterium tuberculosis. RbpA seems to show specificity for the vegetative form of RNA polymerase as opposed to alternative forms of the enzyme. Here, we explain the basis of this specificity by showing that RbpA binds directly to the principal σ subunit in these organisms, but not to more diverged alternative σ factors. Nuclear magnetic resonance spectroscopy revealed that, although differing in their requirement for structural zinc, the RbpA orthologues from S. coelicolor and M. tuberculosis share a common structural core domain, with extensive, apparently disordered, N- and C-terminal regions. The RbpA-σ interaction is mediated by the C-terminal region of RbpA and σ domain 2, and S. coelicolor RbpA mutants that are defective in binding σ are unable to stimulate transcription in vitro and are inactive in vivo. Given that RbpA is essential in M. tuberculosis and critical for growth in S. coelicolor, these data support a model in which RbpA plays a key role in the σ cycle in actinobacteria.
authors.affiliation: School of Life Sciences, University of Sussex, Falmer, Brighton BN1 9QG, UK.
authors.forename: Aline
authors.initials: A
authors.lastname: Tabib-Salazar
authors.forename: Bing
authors.initials: B
authors.lastname: Liu
authors.forename: Philip
authors.initials: P
authors.lastname: Doughty
authors.forename: Richard A
authors.initials: RA
authors.lastname: Lewis
authors.forename: Somadri
authors.initials: S
authors.lastname: Ghosh
authors.forename: Marie-Laure
authors.initials: ML
authors.lastname: Parsy
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Simpson
authors.forename: Kathleen
authors.initials: K
authors.lastname: O'Dwyer
authors.forename: Steve J
authors.initials: SJ
authors.lastname: Matthews
authors.forename: Mark S
authors.initials: MS
authors.lastname: Paget
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D008969:Molecular Sequence Data; D009169:Mycobacterium tuberculosis; D011401:Promoter Regions, Genetic; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D012808:Sigma Factor / Q000378:metabolism*; D048372:Streptomyces coelicolor; D014157:Transcription Factors / Q000737:chemistry* / Q000378:metabolism*; D015533:Transcriptional Activation; D015032:Zinc / Q000032:analysis
chemical_list: D001426:Bacterial Proteins; D012808:Sigma Factor; D014157:Transcription Factors; D015032:Zinc