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Preface/Front Matter

J.C. Wang, N.R. Cozzarelli


Few subjects in biology can claim as broad an intellectual span as can DNA topology. The initial recognition of the formidable challenge that lay in the coiling and uncoiling of the two strands of DNA was made at the same time as the discovery of the double-helical structure of DNA. In the early 1960s, the discovery of double-stranded circular DNA and the finding that both strands of polyomavirus DNA and of SV40 DNA are continuous brought sharply into focus the unique topological problem of the separation of the two multiply-linked, single-stranded DNA rings during replication. The “swivel” requirement in the unlinking of the parental strands provided the impetus for the search for enzymes, now known as DNA topoisomerases, that transform the topology of DNA rings and loops.

Vinograd first had the insight that the three-dimensional shape of a duplex DNA ring is intimately related to the double-helical structure of DNA. He coined the terms “supertwisted,” “superhelical,” and “supercoiled” to describe the sinuous shape of a duplex DNA ring whose topology prevents it from assuming the more stable, relaxed form. Quantitative studies of supercoiled DNA received a boost when it became apparent that a theorem in differential geometry, derived in the late 1960s to describe the twist and writhe of a closed ribbon, was directly applicable to the description of supercoiled DNA.

The discovery of the DNA topoisomerases and their study in the last two decades have firmly established the importance of topology in all aspects of biological transactions involving DNA.

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