title: In vivo inhibition of trypanosome mitochondrial topoisomerase II: effects on kinetoplast DNA maxicircles.
abstract: Kinetoplast DNA, the mitochondrial DNA of trypanosomes, is a topologically complex structure composed of interlocked minicircles and maxicircles. We previously reported that etoposide, a potent inhibitor of topoisomerase II, promotes the cleavage of about 20% of network minicircle DNA (T. A. Shapiro, V. A. Klein, and P. T. Englund, J. Biol. Chem. 264:4173-4178, 1989). We now find that virtually all maxicircles are released from kinetoplast DNA networks after trypanosomes are treated with etoposide. As expected for a topoisomerase II cleavage product, the linearized maxicircles have protein bound to both 5' ends. After etoposide treatment, the residual minicircle catenanes have a sedimentation coefficient which is only 70% that of controls, and by electron microscopy the networks are less compact. Double-size networks, the characteristic dumbbell-shape forms that normally arise in the final stages of network replication, are replaced by aberrant unit-size forms.
authors.affiliation: Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
authors.forename: T A
authors.initials: TA
authors.lastname: Shapiro
authors.forename: A F
authors.initials: AF
authors.lastname: Showalter
mesh_terms: D000818:Animals; D004250:DNA Topoisomerases, Type II / Q000378:metabolism*; D018105:DNA, Kinetoplast / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D005047:Etoposide / Q000494:pharmacology; D046911:Macromolecular Substances; D008854:Microscopy, Electron; D014345:Trypanosoma
chemical_list: D018105:DNA, Kinetoplast; D046911:Macromolecular Substances; D005047:Etoposide; D004250:DNA Topoisomerases, Type II