MTA31ME1JT II - PACE 3 
lt>en two or more proteins act in synergy to form a toxic principle and 
the components are to be cloned separately under conditions that rigor- 
ously preclude the ocmingling of the separate clones, the toxicities of 
each confxx^t nmy be considered individu^dly. 
Restrictions 
1. No specific restriction shedl apply to the cloning of CNA specifying 
a protein if it is non-potent when acteinistered at the level of 
100 vg (or more) per )dJLograni of body weight. 
2. Cloning of Class A, B and C toxins is, for the present, restricted to 
E. ooli host-vector systems. Class A toxins are defined ais those 
that are potent at the level of 1 yg - 100 ygAg body weight. These 
may be cloned in EXl Pi. 
^peci^d Case; 
Some enterotoxins are substantiadly more toxic when administered 
enter 2 dly than parenterally and must be considered separately. The 
following enterotoxins whose effects are confined to the stimulation 
of intestinal secretion that can be entirely reversed by adninistra- 
tion of electrolyte solutions shedl be subject to the rules governing 
Class A toxins. The heat stable toxins of ^ ooli (both STI & STII) 
and of enterooolitica cholera toxin, the heat labile toxins of 
E. ooli , Klebsiella , and other related proteins as may be identified 
that are neutredized by an antisenin monospecific for cholera toxin. 
( 59 ) 
