Persistence of phage λ DNA in genomes of mouse cells transformed by λ-carrying SV40 vectors

Abstract

To test the suitability of simian virus 40 (SV40) DNA as a vector for inserting DNA segments into the chromosomes of mammalian cells, an EcoRI-A fragment of bacteriophage λ DNA was covalently joined to a fragment of SV40 DNA and used to transform mouse cells in culture. Three independent, morphologically transformed clones were obtained that were positive for SV40 T-antigen by immunofluorescence staining. DNA from each transformant was examined by restriction enzyme analysis and found to contain both λ and SV40 sequences. Co-migration of some fragments containing λ and SV40 sequences following digestion of transformed cell DNA by each of four different restriction enzymes indicated that part of the retained λ and SV40 DNA was linked in two of the three lines. In the third line, however, none of the restriction fragments had both λ and SV40 sequences. Although the presence of non-integrated λ DNA was not excluded, at least some of the λ DNA appeared to be linked to host cell DNA. Results of digestion by EcoRI suggested that in some cases the transforming linear molecule had probably circularized prior to integration.