title: Hydroxyl radical footprints and half-site arrangements of binding sites for the CysB transcriptional activator of Salmonella typhimurium.
abstract: CysB is a transcriptional activator for the cysteine regulon and negatively autoregulates its own gene, cysB. Transcription activation also requires an inducer, N-acetyl-L-serine. CysB is known to bind to activation sites just upstream of the -35 regions of the positively regulated cysJIH, cysK, and cysP promoters and to a repressor site centered at about +1 in the cysB promoter. Additional accessory sites have been found in positively regulated promoters. The hydroxyl radical footprinting experiments reported here indicate that the activation sites CBS-J1, CBS-K1, and CBS-P1 in the cysJIH, cysK, and cysP promoters are composed of two convergently oriented 19-bp half-sites separated by 1 or 2 bp. N-Acetyl-L-serine stimulates binding to these sites as well as to the accessory sites CBS-J2 and CBS-P2, both of which share a similar topology with activation sites. A second topology is found in the accessory site CBS-K2 and the repressor site CBS-B, which contain divergently oriented 19-bp half-sites separated by one or two helical turns. N-Acetyl-L-serine inhibits binding to these two sites. A third topology is present in the cysK and cysP promoters, where an additional half-site is oriented toward the activation site and separated from it by one helical turn. Here, CysB binds to all three half-sites, bending the DNA, and N-acetyl-L-serine decreases the extent of bending. The marked dissimilarities of these half-site arrangements and of their responses to N-acetyl-L-serine suggest that CysB, a homotetramer, binds to them with different combinations of subunits.
authors.affiliation: Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710, USA.
authors.forename: M M
authors.initials: MM
authors.lastname: Hryniewicz
authors.forename: N M
authors.initials: NM
authors.lastname: Kredich
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites / Q000187:drug effects / Q000235:genetics; D003545:Cysteine / Q000096:biosynthesis; D004269:DNA, Bacterial / Q000187:drug effects / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D017665:Hydroxyl Radical / Q000494:pharmacology; D008957:Models, Genetic; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation / Q000187:drug effects; D011401:Promoter Regions, Genetic / Q000187:drug effects / Q000235:genetics*; D011485:Protein Binding / Q000235:genetics; D011487:Protein Conformation; D012486:Salmonella typhimurium / Q000235:genetics*; D012694:Serine / Q000031:analogs & derivatives / Q000494:pharmacology; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; C062886:CysB protein, Bacteria; C489265:CysB protein, Salmonella typhimurium; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D014157:Transcription Factors; D017665:Hydroxyl Radical; D012694:Serine; D003545:Cysteine; C012162:N-acetylserine