A Dye-Buoyant-Density Method for the Detection and Isolation of Closed Circular Duplex DNA: The Closed Circular DNA in HeLa Cells

Abstract

Covalently closed circular duplex DNA’s are now known to be widespread among living organisms. This DNA structure, originally identified in polyoma viral DNA,^1’2 has been assigned to the mitochondrial DNA’s in ox³ and sheep heart,⁴ in mouse and chicken liver,³ and in unfertilized sea urchin egg.⁵ The animal viral DNA’s—polyoma, SV40,⁶ rabbit⁷ and human⁸ papilloma—the intracellular forms of the bacterial viral DNA’s—φX174,^{9, 10} lambda,^{11, 12} M13,¹³ and P22¹⁴—and a bacterial plasmid DNA, the colicinogenic factor E₂,¹⁵ have all been shown to exist as closed circular duplexes. Other mitochondrial DNA’s^{16, 17} and a portion of the DNA from boar sperm¹⁸ have been reported to be circular, but as yet have not been shown to be covalently closed.