The structural gene for tetanus neurotoxin is on a plasmid

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Tetanus toxin is a potent neurotoxin produced by Clostridium tetani.
• The genetic basis and location of the tetanus toxin gene were previously unclear.

Purpose of the Study:

• To determine if the structural gene for tetanus toxin is located on a plasmid.
• To map the location and orientation of the tetanus toxin gene on the plasmid.

Main Methods:

• A synthetic oligonucleotide probe was designed based on the amino-terminal amino acid sequence of tetanus toxin.
• The probe was used to hybridize with plasmid DNA from toxigenic and nontoxigenic Clostridium tetani strains.
• Restriction endonuclease cleavage mapping was performed on plasmids pCL1 and pCL2.

Main Results:

• The synthetic probe hybridized to plasmid DNA from toxigenic strains but not nontoxigenic strains, indicating the gene is plasmid-borne.
• A spontaneous deletion in plasmid pCL2 resulted in nontoxigenicity, but the probe still hybridized, showing the amino-terminal coding region was intact.
• Cleavage maps of pCL1 and pCL2 provided the approximate location and orientation of the toxin's structural gene.

Conclusions:

• The structural gene for tetanus toxin is located on a plasmid in Clostridium tetani.
• The deletion of specific DNA regions on the plasmid leads to a loss of toxin production.
• The study successfully mapped the tetanus toxin gene on the plasmid using molecular probes and restriction mapping.