APPENDIX H 
candidate, which in case of culture overgrowth for 24 hours may reach 
- 6 
a level of persistent association of about 10 associations per fragment- 
containing vector. Thus, production of fragments with these vectors 
-2 
should be limited to hosts offering a factor of safety of at least 10 
A minimal test for any proposed partially disabled host, however, will 
include a measure of the reversion frequencies for each of the relevant 
mutations. 
Although killing by chloroform decreases the probability of survival 
of any clone -containing bacteria by many orders of magnitude, this 
factor is not included in calculating the degree of biological containment 
measured in this test. 
C. The frequency of survival of fragment -transferring capacity 
_ 
of a vector phage carrying a model fragment should be less t han 1 0 
in the tests specified below . 
It is understood that this value (as in B) should represent the 
product of the following probabilities: 
(1 ) The probability that the phage will survive until it meets a 
sensitive host. 
(2) The probability that (a) the fragment will persist in a non- 
permissive X -sensitive heteroimmune lysogen or (b) that the fragment- 
containing vector phage will acquire genetic material from a related 
prophage that will serve to negate the safety features of Lhe vector. 
Comments: 
-3 
Data available for wild -type ^ suggest that (1) is less than 10 
-5 
Theoretically then, the value for (2) must be 10 or less. 
Appendix H — 3 
