ATTACHMENT II - PACE 4 
3. Class B toxins are those that are potent at the level of 100 ng - 
1000 ng/kg body weight (exan^les - di^^theria toxin, Clostridium 
perfringens , epsilon toxin, abrin). DNA for these proteins may be 
cloned EK2/P2 or EK1/P3. 
4 . Qass C toxins are potent at less than 100 ng, namely the botulinum 
toxins, tetanus toxin, and 9iigella dysenteriae neurotoxin. Cloning 
of genes for these toxins is restricted but exceptions will be consi- 
dered on a case-by-case basis by RAC following publication of the 
request in the Federal Register. It is likely that permission to 
proceed with some protocols involving toxins of this class will require 
the work to proceed in a P4 facility. 
Footnote; 
It is conceivable that sane toxins may greatly 100-fold) potentiate the 
effects of other toxins. If information on potentiation becomes available, 
the toxins with potentiating effects on other toxins will oo:istitute a 
special situation to be considered on a case-by-case basis as a minor 
action. 
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