Infectivity in mouse fibroblasts of polyoma DNA integrated into plasmid pBR322 or lambdoid phage DNA

Abstract

THERE has been much speculation on the possible hazards of hybrid DNA technology¹. An important question in this context is whether a viral DNA, covalently linked to a vector, can be transferred from within a bacterium into an animal cell, either in vitro or in vivo, and initiate viral infection. As a first step, it is necessary to determine whether a hybrid containing eukaryotic viral DNA can, on penetration into a permisive cell, give rise to virus formation, as is the case for hybrids containing a prokaryotic viral sequence². As part of a risk-testing programme sponsored by EMBO, this question was investigated with mouse polyoma virus DNA. Polyoma virus will grow readily in mice; infection can be initiated by a single infectious particle as well as by naked viral DNA, and can be easily detected by monitoring the production of anti-viral antibodies. Virus production, and not tumour formation, was chosen as a criterion for biological activity because although polyoma virus will transform cells in vitro, tumours are produced in vivo only when large quantities of virus are inoculated into immunologically immature or immunosuppressed animals. We describe here the construction and characterisation of various plasmid pBR322 and phage λ derivatives containing polyoma DNA and their infectivity towards mouse fibroblast cells. The only recombinant molecules so far obtained which were infective as intact molecules were plasmids with dimeric polyoma DNA inserts.