38 
of eukaryotic DNA whose function has been established, 
which does not code for a toxic product, and which has 
been previously cloned in a prokaryotic host-vector 
system. 
£. A recombinant DNA molecule consisting of defective SV40 
DNA lacking substantial segments of the late region, 
plus DNA from non-pathogenic organisms or Class I 
viruses (5), can be propagated as an autonomous cellular 
element in established lines of cells under P3 conditions 
provided that there is no exogenous or endogenous helper, 
and that it is demonstrated that n£ infectious virus 
particles are being produced. Until this has been 
demonstrated, the appropriate containment conditions 
specified in 2. d_. and 2_. b_. shall be used. 
d_. Recombinant DNA molecules consisting of defective SV40 
DNA and sequences from non-pathogenic prokaryotic or 
eukaryotic organisms or Class I viruses (5) can be 
used to transform established lines of non-permissive 
cells under P3 conditions. It must be demonstrated that 
no infectious virus particles are being produced; rescue 
of SV40 from such transformed cells by co-cultivation 
or transfection techniques must be carried out in P4 
condi tions . 
3_. Efforts should be made to ensure that all cell lines are 
free of virus particles and mycoplasma. 
Since SV40 and polyoma are limited in their scope to 
act as vectors, chiefly because the amount of foreign DNA 
[ 109 ] 
