title: Functions of the sigma(54) region I in trans and implications for transcription activation.
abstract: Control of transcription frequently involves the direct interaction of activators with RNA polymerase. In bacteria, the formation of stable open promoter complexes by the sigma(54) RNA polymerase is critically dependent on sigma(54) amino Region I sequences. Their presence correlates with activator dependence, and removal allows the holoenzyme to engage productively with melted DNA independently of the activator. Using purified Region I sequences and holoenzymes containing full-length or Region I-deleted sigma(54), we have explored the involvement of Region I in transcription activation. Results show that Region I in trans inhibits a reversible conformational change in the holoenzyme believed to be polymerase isomerization. Evidence is presented indicating that the holoenzyme (and not the promoter DNA per se) is one interacting target used by Region I in preventing polymerase isomerization. Activator overcomes this inhibition in a reaction requiring nucleotide hydrolysis. Region I in trans is able to inhibit activated transcription by the holoenzyme containing full-length sigma(54). Inhibition appeared to be noncompetitive with respect to the activator, suggesting that a direct activator interaction occurs with parts of the holoenzyme outside Region I. Stabilization of isomerized holoenzyme bound to melted DNA by Region I in trans occurs largely independently of the initiating nucleotide, suggesting a role for Region I in maintaining the open complex.
authors.affiliation: Department of Biology, Imperial College of Science Technology and Medicine, Sir Alexander Fleming Building, Imperial College Road, London SW7 2AZ, United Kingdom.
authors.forename: M T
authors.initials: MT
authors.lastname: Gallegos
authors.forename: W V
authors.initials: WV
authors.lastname: Cannon
authors.forename: M
authors.initials: M
authors.lastname: Buck
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins; D012321:DNA-Directed RNA Polymerases / Q000235:genetics* / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D051877:RNA Polymerase Sigma 54; D012808:Sigma Factor / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic; D015533:Transcriptional Activation
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D012808:Sigma Factor; C497751:rpoN protein, E coli; D012321:DNA-Directed RNA Polymerases; D051877:RNA Polymerase Sigma 54