ABSTRACT

Gene amplification (GA) is the mechanism by which transformed cells generate multiple copies of discrete regions of their genome, with a resulting increase in titers of gene product(s) coded for within the amplified region. A can produce resistance to antineoplastic drugs in culture, and has been implicated in tumor progression in vivo. Episomes containing both amplified drug resistance genes and oncogenes have been detected and characterized in tumor cell lines by alkaline lysis followed by agarose gel electrophoresis at high electric field strengths. This technique specifically detects supercoiled circular episomal DNA, although circular DNA can exist in both supercoiled and relaxed forms. Circular DNA molecules can exist in both supercoiled and relaxed topologies which complicates their detection and characterization. Three different electrophoretic strategies were compared for their relative efficiencies in the detection and characterization of episomal DNA from alkaline lysates: high voltage electrophoresis (HiVE), low voltage electrophoresis (LoVE), and field-inversion gel electrophoresis (FIGE).