Characterization of supercoiled oligomeric SV40 DNA molecules in productively infected cells

Abstract

We have characterized oligomeric supercoiled forms of SV40 DNA which appear during the latter stages of productive infection and account for more than 10% of the intracellular viral DNA 70 hr after infection. These DNA molecules form a series of oligomers that are integral multiples (dimers through hexamers) of supercoiled SV40 DNA. We have determined the sedimentation constants of oligomeric DNA under neutral and alkaline conditions and ascertained electrophoretic mobilities of the different supercoiled forms. Nucleic acid hybridization studies as well as cleavage with bacterial restriction endonucleases both indicate that oligmeric supercoiled DNA molecules contain only SV40 DNA sequences. These unintegrated viral DNA forms appear predominantly in the Hirt pellet and sediment in regions of alkaline sucrose gradients characteristic of high molecular weight cellular DNA.