Size and distribution of SV 40 DNA Sequences covalently linked with the DNA of permissive mammalian cells

CV-1 cells productively infected with SV 40 contain viral DNA which is covalently linked with the host cell DNA. These linear duplex viral-host DNA molecules are replicated during the infectious cycle. They can be selectively isolated and purified by two successive cycles of DNA-DNA hybridization and elution steps using first CV-1 cell and then SV 40-DNA immobilized on filters. In an attempt to clarify the nature of the host DNA sequences neighbouring the viral DNA it was found that reiterated host DNA must be within the range of 800 bases from the viral sequences. Reassociation kinetics and treatment of the reassociated viral-host DNA sequences with single strand-specific S1 nuclease have shown that unique host DNA sequences are always present in close neighbourhood of the viral DNA. Most of the SV 40 DNA sequences are probably intergrated as fragments of subgenomic length.

Fate of infecting simian virus 40-deoxyribonucleic acid in nonpermissive cells: integration into host deoxyribonucleic acid

Nonpermissive 3T3 cells were infected with purified superhelical simian virus 40 (SV40) deoxyribonucleic acid I (DNA I). One hour after infection, approximately 60% of the intracellular SV40 DNA was converted to relaxed forms. One day after infection, all intracellular SV40 DNA was present as slow-sedimenting material, and no SV40 DNA I was detectable. At 2 days after infection there appeared viral DNA sequences cosedimenting with cellular DNA during alkaline velocity centrifugation. Furthermore, by both alkaline equilibrium gradient centrifugation and by DNA-ribonucleic acid hybridization analysis, covalent linkage of viral DNA sequences to cellular DNA was demonstrated. Integration of SV40 DNA into cellular DNA did not appear to require DNA synthesis, although DNA synthesis followed by mitotic division of the cells enhanced the amount of viral DNA integrated. Based on data obtained by two different methods, it was calculated that 1,100 to 1,200 SV40 DNA equivalents must be integrated per cell by 48 hr after infection.

Identification of virus-induced proteins in cells productively infected with simian virus 40

The number and molecular weight of the structural polypeptides of highly purified simian virus 40 (SV40) were determined by polyacrylamide gel electrophoresis. Six different polypeptides were found, two of which (VP1 and VP2) comprise the bulk of the viral capsid proteins. The pattern of protein synthesis in productively infected CV-1 cells was studied by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Identification of virus-induced proteins in the infected CV-1 cells was achieved in double-labeling experiments by electrophoresis with purified labeled SV40 capsid proteins. Four of these proteins (VP1 and VP4) could be classified as components of the virion because their synthesis occurred after the onset of viral deoxyribonucleic acid (DNA) replication and because they were inhibited by arabinofuranosylcytosine (ara-C). Appearance of two other virus-induced proteins was not prevented by ara-C; one of them did not comigrate in the electrophoresis with purified virion polypeptides, and both could be detected before the onset of viral DNA synthesis. These latter two proteins were classified on the basis of these criteria as nonvirion capsid proteins (NCVP1 and NCVP2).

Initial stage of transformation of permissive cells by simian virus 40: development of resistance to productive infection

A quantitative assay has been used to determine the conditions leading to acquisition of resistance of permissive cells to lytic infection. The number of cell colonies surviving infection depends on the occurrence of several cell divisions after infection. High yields of resistant colonies were obtained when infected, confluent cultures were released from contact inhibition 10 to 14 hr after infection. Infection of actively growing cells produced similar results, but halting further division by seeding these growing cells on confluent monolayers prevented the development of colonies. Colony formation was a direct function of multiplicities lower than 5. An inverse killing response was observed with higher multiplicities, yet colonies were produced at a multiplicity of infection as high as 50. Brief exposure of input simian virus 40 to ultraviolet light stimulated colony formation. Irradiation of the virus for longer periods of time led to reduction of colony formation at a rate slower than the rate of inactivation of viral infectivity. It was concluded that resistance is induced by simian virus 40 and that this alteration represents one of the earliest detectable characteristics of the transformation of permissive cells.