Molecular cloning of polyoma virus DNA in Escherichia coli: oncogenicity testing in hamsters.

Inoculation of suckling hamsters with 2 x 10(8) live cells of Escherichia coli K12 strain chi1776, carrying the complete genome of polyoma virus in a recombinant plasmid, failed to induce tumors in any of 32 recipients. Also, lambda phage DNA and particles with a monomeric insert of polyoma DNA did not induce tumors. Purified recombinant plasmid DNA, as well as phage particles and DNA containing a head-to-tail dimer of polyoma DNA, showed a low degree of oncogenicity, comparable to that of polyoma DNA prepared from mouse cells. These findings support the previous conclusions, based on infectivity assays in mice, that propagation of polyoma virus DNA as a component of recombinant DNA molecules in E. coli K12 reduces its biologic activity many orders of magnitude relative to the virus itself.