DNA of bacteriophage PM2: a closed circular double-stranded molecule.

The DNA molecules isolated from mature bacteriophage PM2 are closed double-stranded rings of a molecular weight of six million. Direct evidence for the circularity and supercoiling of PM2 DNA was obtained by electron microscopy. Other properties, such as sedimentation behavior at neutral and alkaline pH, unusually high buoyant density in alkaline CsCl, and stability upon heating, are consistent with this structure. Only the four common nucleotides are found after hydrolysis and chromatographic analysis of PM2 DNA.