The attachment of minicircles to kinetoplast DNA networks during replication

Kinetoplast DNA (kDNA), the trypanosomatid mitochondrial DNA, is a network containing several thousand interlocked minicircles. During kDNA synthesis, minicircles dissociate from the network, and after replication their progeny reattach to the network periphery. Using electron microscopy autoradiography, we found that newly synthesized 3H-labeled minicircles, after short labeling periods, are concentrated in two peripheral zones on opposite sides of the network. These must be minicircle attachment sites, adjacent to the two diametrically opposed complexes of replication proteins observed previously. From the pattern of radiolabeling during longer pulses, we reached the unexpected conclusion that minicircle attachment around the entire network periphery may be due to a relative movement of the kinetoplast and the two complexes. The kinetoplast probably rotates between two fixed complexes.