Isolation of a Type I Topoisomerase from Carrot Cells

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Abstract
Carbonera, D., Cella, R., Montecucco, A. and Ciarrocchi, G. 1988. Isolation of a type I topoisomerase from carrot cells.—J. exp. Bot. 39: 70–78. A DNA topoisomerase activity has been isolated from suspension-cultured cells of Daucus carota, the enzyme has been chromatographed on CM-cellulose, DNA-cellulose and Sephadex G100. Its Mr appears to be about 100000 by gel filtration. Carrot DNA topoisomerase relaxes both positively and negatively supercoiled DNA by changing the linking number of the substrate in steps of one and is not able to unknot the knotted P4 DNA. It does not require ATP or Mg2+ , has an optimal salt concentration between 40 and 120 mol m−3 KCl and is resistant to nalidixic acid and novobiocine. This carrot enzyme can be designated as a eukaryotic type I DNA topoisomerase.