The fate of a bacterial plasmid in mammalian cells.

When hamster cells are infected with the bacterial plasmid colicinogenic factor E1 (ColE1), as much as 5-8% of the input plasmid radioactivity is found in the recipient cell, mainly in the nuclear fraction. Density shift experiments with bromodeoxyuridine labeled ColE1 DNA indicate that part of the input DNA may be replicated in the nucleus. ColE1 specific RNA but no colicin E1, can be detected during the first two generations after the uptake of ColE1 DNA. However, extrachromosomal ColE1 DNA is unstable in the mammalian cells and is degraded to acid soluble fragments after a few generations.