title: Isolation and characterization of mutations in region 1.2 of Escherichia coli sigma70.
abstract: Eubacterial RNA polymerase uses the sigma (sigma) subunit for recognition of and transcription initiation from promoter DNA sequences. One family of sigma factors includes those related to the primary sigma factor from Escherichia coli, sigma70. Members of the sigma70 family have four highly conserved domains, of which regions 2 to 4 are present in all members. Region 1 can be subdivided into regions 1.1 and 1.2. Region 1.1 affects DNA binding by sigma70 alone, as well as transcription initiation by holoenzyme. Region 1.2, present and highly conserved in most sigma factors, has not yet been assigned a putative function, although previous work has demonstrated that it is not required for either association with the core subunits of RNA polymerase or promoter-specific binding by holoenzyme. We generated random single amino acid substitutions targeted to region 1.2 of E. coli sigma70 as well as a deletion of region 1.2, and characterized the behaviour of the mutant sigma factors both in vivo and in vitro to investigate the function of region 1.2 during transcription initiation. In this study, we show that mutations in region 1.2 can affect promoter binding, open complex and initiated complex formation and the transition from abortive transcription to elongation.
authors.affiliation: Department of Microbiology and Molecular Genetics, The University of Texas Health Science Center, 6431 Fannin JFB 1.765, Houston, TX 77030, USA.
authors.forename: N E
authors.initials: NE
authors.lastname: Baldwin
authors.forename: A J
authors.initials: AJ
authors.lastname: Dombroski
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D010582:Bacteriophage lambda / Q000235:genetics; D017124:Conserved Sequence; D004247:DNA / Q000235:genetics / Q000378:metabolism; D018983:DNA Footprinting; D012321:DNA-Directed RNA Polymerases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D003850:Deoxyribonuclease I / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D005816:Genetic Complementation Test; D020035:Holoenzymes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D010641:Phenotype; D017354:Point Mutation / Q000235:genetics*; D011196:Potassium Permanganate / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D021122:Protein Subunits; D012808:Sigma Factor / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D029968:Escherichia coli Proteins; D020035:Holoenzymes; D021122:Protein Subunits; D012808:Sigma Factor; D011196:Potassium Permanganate; D004247:DNA; C081775:RNA polymerase sigma 70; D012321:DNA-Directed RNA Polymerases; D003850:Deoxyribonuclease I