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.
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.
Raffestin
Stéphanie
S
Institut Pasteur, Unité des Bactéries Anaérobies et Toxines, 25-28 rue du Dr Roux 75724, Paris cedex 15, France.
Dupuy
Bruno
B
Marvaud
Jean Christophe
JC
Popoff
Michel R
MR
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*
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