title: Transcriptional takeover by sigma appropriation: remodelling of the sigma70 subunit of Escherichia coli RNA polymerase by the bacteriophage T4 activator MotA and co-activator AsiA.
abstract: Activation of bacteriophage T4 middle promoters, which occurs about 1 min after infection, uses two phage-encoded factors that change the promoter specificity of the host RNA polymerase. These phage factors, the MotA activator and the AsiA co-activator, interact with the sigma(70) specificity subunit of Escherichia coli RNA polymerase, which normally contacts the -10 and -35 regions of host promoter DNA. Like host promoters, T4 middle promoters have a good match to the canonical sigma(70) DNA element located in the -10 region. However, instead of the sigma(70) DNA recognition element in the promoter's -35 region, they have a 9 bp sequence (a MotA box) centred at -30, which is bound by MotA. Recent work has begun to provide information about the MotA/AsiA system at a detailed molecular level. Accumulated evidence suggests that the presence of MotA and AsiA reconfigures protein-DNA contacts in the upstream promoter sequences, without significantly affecting the contacts of sigma(70) with the -10 region. This type of activation, which is called 'sigma appropriation', is fundamentally different from other well-characterized models of prokaryotic activation in which an activator frequently serves to force sigma(70) to contact a less than ideal -35 DNA element. This review summarizes the interactions of AsiA and MotA with sigma(70), and discusses how these interactions accomplish the switch to T4 middle promoters by inhibiting the typical contacts of the C-terminal region of sigma(70), region 4, with the host -35 DNA element and with other subunits of polymerase.
authors.affiliation: Laboratory of Molecular and Cellular Biology, National Institute of Diabetes Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, USA.
authors.forename: Deborah M
authors.initials: DM
authors.lastname: Hinton
authors.affiliation: Laboratory of Molecular and Cellular Biology, National Institute of Diabetes Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, USA.
authors.forename: Suchira
authors.initials: S
authors.lastname: Pande
authors.affiliation: Laboratory of Molecular and Cellular Biology, National Institute of Diabetes Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, USA.
authors.forename: Neelowfar
authors.initials: N
authors.lastname: Wais
authors.affiliation: Laboratory of Molecular and Cellular Biology, National Institute of Diabetes Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, USA.
authors.forename: Xanthia B
authors.initials: XB
authors.lastname: Johnson
authors.affiliation: Laboratory of Molecular and Cellular Biology, National Institute of Diabetes Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, USA.
authors.forename: Madhavi
authors.initials: M
authors.lastname: Vuthoori
authors.affiliation: Laboratory of Molecular and Cellular Biology, National Institute of Diabetes Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, USA.
authors.forename: Anna
authors.initials: A
authors.lastname: Makela
authors.affiliation: Laboratory of Molecular and Cellular Biology, National Institute of Diabetes Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, USA.
authors.forename: India
authors.initials: I
authors.lastname: Hook-Barnard
mesh_terms: D004268:DNA-Binding Proteins / Q000502:physiology*; D012321:DNA-Directed RNA Polymerases / Q000502:physiology*; D004926:Escherichia coli / Q000378:metabolism / Q000821:virology*; D011401:Promoter Regions, Genetic; D012808:Sigma Factor / Q000502:physiology*; D014157:Transcription Factors / Q000502:physiology*; D014158:Transcription, Genetic; D014764:Viral Proteins / Q000502:physiology*
chemical_list: C078876:AsiA protein, Enterobacteria phage T4; D004268:DNA-Binding Proteins; C067996:MotA protein, Enterobacteria phage T4; D012808:Sigma Factor; D014157:Transcription Factors; D014764:Viral Proteins; C081775:RNA polymerase sigma 70; D012321:DNA-Directed RNA Polymerases