Aspects of the secondary and tertiary structure of DNA.

DNA is the primary genetic material of most organisms. A wide variety of naturally occurring duplex DNA's are known to exist as covalently closed circles. This covalent continuity introduces a topological constraint, and consequently these molecules possess aspects of tertiary and even higher-order structure. Virtually every physical, chemical and biological property of DNA - its transcription, hydrodynamic behaviour, energetics, enzymology and so on - are related to these structural features. We describe the parameters describing the topology and conformation of covalently-closed, duplex DNA's (form I DNA's), the conservation relationship between them and its implications.