title: BotR/A and TetR are alternative RNA polymerase sigma factors controlling the expression of the neurotoxin and associated protein genes in Clostridium botulinum type A and Clostridium tetani.
abstract: Clostridium botulinum and Clostridium tetani, respectively, produce potent toxins, botulinum neurotoxin (BoNT) and tetanus neurotoxin (TeTx), which are responsible for severe diseases, botulism and tetanus. Neurotoxin synthesis is a regulated process in Clostridium. The genes botR/A in C. botulinum A and tetR in C. tetani positively regulate expression of BoNT/A and associated non-toxic proteins (ANTPs), as well as TeTx respectively. The botR/A gene lies in close vicinity of the two operons which contain bont/A and antps genes in C. botulinum A, and tetR immediately precedes the tetX gene in C. tetani. We show that BotR/A and TetR function as specific alternative sigma factors rather than positive regulators based on the following results: (i) BotR/A and TetR associated with target DNAs only in the presence of the RNA polymerase core enzyme (Core), (ii) BotR/A and TetR directly bound with the core enzyme, (iii) BotR/A-Core recognized -35 and -10 regions of ntnh-bont/A promoter and (iv) BotR/A and TetR triggered in vitro transcription from the target promoters. In C. botulinum A, bont/A and antps genes are transcribed as bi- and tricistronic operons controlled by BotR/A. BotR/A and TetR are seemingly related to a new subgroup of the sigma70 family that includes TcdR and UviA, which, respectively, regulate production of toxins A and B in C. difficile and bacteriocin in C. perfringens. Sequences of -35 region are highly conserved in the promoter of target toxin genes in C. botulinum, C. tetani, C. difficile and C. perfringens. Overall, a common regulation mechanism probably controls toxin gene expression in these four toxigenic clostridial species.
authors.affiliation: Institut Pasteur, Unité des Bactéries Anaérobies et Toxines, 25-28 rue du Dr Roux 75724, Paris cedex 15, France.
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Raffestin
authors.forename: Bruno
authors.initials: B
authors.lastname: Dupuy
authors.forename: Jean Christophe
authors.initials: JC
authors.lastname: Marvaud
authors.forename: Michel R
authors.initials: MR
authors.lastname: Popoff
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology*; D001483:Base Sequence; D001905:Botulinum Toxins / Q000235:genetics*; D003014:Clostridium botulinum / Q000235:genetics / Q000502:physiology*; D003017:Clostridium tetani / Q000235:genetics / Q000502:physiology*; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D012321:DNA-Directed RNA Polymerases / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D012808:Sigma Factor / Q000235:genetics / Q000502:physiology*; D013744:Tetanus Toxin / Q000235:genetics*; D015534:Trans-Activators / Q000235:genetics / Q000502:physiology*
chemical_list: D001426:Bacterial Proteins; C116103:BotR protein, Clostridium botulinum; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D012808:Sigma Factor; C116102:TetR protein, Clostridium tetani; D013744:Tetanus Toxin; D015534:Trans-Activators; C081775:RNA polymerase sigma 70; D012321:DNA-Directed RNA Polymerases; D001905:Botulinum Toxins