TetR is a positive regulator of the tetanus toxin gene in Clostridium tetani and is homologous to BotR

The TetR gene immediately upstream from the tetanus toxin (TeTx) gene was c haracterized. It encodes a 21,562-Da protein which is related (50 to 65% id entity) to the equivalent genes (botR) in Clostridium botulinum. TetR has t he feature of a DNA binding protein with a basic pi (9.53). It contains a h elix-turn-helix motif and shows 29% identity with other putative regulatory genes in Clostridium, i.e., uviA from C. perfringens and txeR from C. diff icile. We report for the first time the transformation of C. tetani by elec troporation, which permitted us to investigate the function of tetR. Overex pression of tetR in C. tetani induced an increase in TeTx production and in the level of the corresponding mRNA. This indicates that TetR is a transcr iptional activator of the TeTx gene. Overexpression of botR/A (60% identity with TetR at the amino acid level) in C tetani induced an increase in TeTx production comparable to that for overexpression of tefR. However, botR/C (50% identity with TetR at the amino acid level) was less efficient. This s upports that TetR positively regulates the TeTx gene in C. tetani and that a conserved mechanism of regulation of the neurotoxin genes is involved in C. tetani and C. botulinum.