title: Mutant forms of Salmonella typhimurium sigma54 defective in transcription initiation but not promoter binding activity.
abstract: Transcription initiation with sigma54-RNA polymerase holoenzyme (sigma54-holoenzyme) has absolute requirements for an activator protein and ATP hydrolysis. sigma54's binding to core RNA polymerase and promoter DNA has been well studied, but little is known about its role in the subsequent steps of transcription initiation. Following random mutagenesis, we isolated eight mutant forms of Salmonella typhimurium sigma54 that were deficient in transcription initiation but still directed sigma54-holoenzyme to the promoter to form a closed complex. Four of these mutant proteins had amino acid substitutions in region I, which had been shown previously to be required for sigma54-holoenzyme to respond to the activator. From the remaining mutants, we identified four residues in region III which when altered affect the function of sigma54 at some point after closed-complex formation. These results suggest that in addition to its role in core and DNA binding, region III participates in one or more steps of transcription initiation that follow closed-complex formation.
authors.affiliation: Department of Microbiology, University of Georgia, Athens, Georgia 30602, USA.
authors.forename: M T
authors.initials: MT
authors.lastname: Kelly
authors.forename: T R
authors.initials: TR
authors.lastname: Hoover
mesh_terms: D000483:Alleles; D019943:Amino Acid Substitution; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D017100:Bacteriophage P22 / Q000235:genetics; D004252:DNA Mutational Analysis; D015342:DNA Probes / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D012321:DNA-Directed RNA Polymerases / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D017930:Genes, Reporter / Q000235:genetics; D005974:Glutamate-Ammonia Ligase / Q000235:genetics / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism; D020035:Holoenzymes / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011485:Protein Binding; D051877:RNA Polymerase Sigma 54; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D012486:Salmonella typhimurium / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000235:genetics*
chemical_list: D001426:Bacterial Proteins; D015342:DNA Probes; D004268:DNA-Binding Proteins; D020035:Holoenzymes; D012097:Repressor Proteins; D012808:Sigma Factor; D005973:Glutamine; D012321:DNA-Directed RNA Polymerases; D051877:RNA Polymerase Sigma 54; D005974:Glutamate-Ammonia Ligase