Escherichia
coli cells containing a recombinant plasmid with three tandem
inserts of simian virus 40 DNA were able to infect CV-1 monkey
cells under various conditions.
The gene transfer was resistant
to DNase I and therefore seems not to occur via free DNA but
most likely via uptake of whole bacteria, followed by release
of plasmid DNA and generation of infectious circular simian
virus 40 DNA in a recombination-excision process. Spontaneous
transfer was found to be infrequent, 4 X 109 bacteria yielding
one infection per 107 monkey cells. The frequency was greatly
increased by adding bacteria as a calcium phosphate coprecipitate
or by fusion of lysozyme-treated bacteria (protoplasts)
with monkey cells in the presence of polyethylene glycoL