Electron microscopic evidence for the cruciform structure in intracellular SV40 DNA.

The conformation of intracellular SV40 DNA during lytic infection of CV-1 cells was studied by the psoralen crosslinking technique. Analysis of the crosslinked SV40 DNA in the electron microscope revealed a rare population (0.1%) with a cruciform structure at coordinates 0.62 +/- 0.05 or at 0.37 +/- 0.05 of the SV40 genome. The implication of this observation in relation to SV40 DNA replication is discussed.