The structure of the kinetoplast DNA of Trypanosoma equiperdum has been studied and compared to the structure of the circular mitochondrial DNA extracted from a dyskinetoplastic strain of T. equiperdum. In T. equiperdum wild type, the kinetoplast DNA constitutes approximately 6% of the total cellular DNA and is composed of approximately 3,000 supercoiled minicircles of 6.4 x 10(5) daltons and approximately 50 circular supercoiled molecules of 15.4 x 10(6) daltons topologically interlocked; The buoyant density in CsCl of the minicircles is 1.691 g/cm 3. The large circles have a buoyant density of 1.684 g/cm 3, are homogeneous in size and are selectively cleaved by several restriction endonucleases which do not cleave the minicircles. The cleavage sites of six different restriction endonucleases have been mapped on the large circle. The minicircles are cleaved by two other restriction endonucleases, and their cleavage sites have been mapped. The mitochondrial DNA extracted from the dyskinetoplastic strain of T. equiperdum represents 7% of the total DNA of the cell and is composed of supercoiled circles, heterogeneous in size, and topologically associated in catenated oligomers. Its buoyant density in CsCl is 1.688 g/cm 3. These molecules are not cleaved by any of the eight restriction endonucleases tested. The reassociation kinetics of in vitro labeled kDNA minicircles and large circles has been studied. The results indicate that the minicircles as well as the large circles are homogeneous in sequence and that the circular DNA of the dyskinetoplastic strain has no sequence in common with the kDNA of the wild strain.

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