MITOCHONDRIAL-DNA OF KINETOPLASTIDS

This chapter highlights mitochondrial DNA of kinetoplastids. Kinetoplast DNA (kDNA) is the unusual mitochondrial DNA characteristic of members of Kinetoplastida. This DNA has two distinctive general features—namely, (1) it comprises two classes of unrelated circular molecules, maxicircles and minicircles, and (2) in each cell these molecules are catenated into a single massive network. The kDNA is located within an enlarged region of the mitochondrion, also called the “kinetoplast,” opposite the flagellar basal body. The kDNA network has a highly ordered structure. The network is formed by catenation of the maxicircles and minicircles. The sizes of both the maxicircle and the minicircle vary among species. The size differences reflect variation in the size and presumably repeat number of simple repeated sequences in one region, termed the “variable region.” Minicircles decatenate from the network and replicate by a conventional mechanism that entails the formation of theta structure intermediates. The replicated minicircles then reattach to the network. The detachment and reattachment appears to entail topoisomerase II activity. Maxicircle replication appears to entail a rolling circle mechanism. © 1992, Academic Press Inc.