Intramitochondrial location and dynamics of Crithidia fasciculata kinetoplast minicircle replication intermediates

Kinetoplast DNA, the mitochondrial DNA of Crithidia fasciculata, is organiz ed into a network containing 5,000 topologically interlocked minicircles. T his network, situated within the mitochondrial matrix, is condensed into a disk-shaped structure located near the basal body of the flagellum. Fluores cence in situ hybridization revealed that before their replication, minicir cles are released vectorially from the network face nearest the flagellum. Replication initiates in the zone between the flagellar face of the disk an d the mitochondrial membrane (we term this region the kinetoflagellar zone [KFZ]). The replicating minicircles then move to two antipodal sites that f lank the disk-shaped network. In later stages of replication, the number of free minicircles increases, accumulating transiently in the KFZ. The final replication events, including primer removal, repair of many of the gaps, and reattachment of the progeny minicircles to the network periphery, are t hought to take place within the antipodal sites.