kinetoplasts

Kinetoplasts are a distinctive mitochondrial structure found in kinetoplastid protozoa, a group that includes parasites such as Trypanosoma and Leishmania. The kinetoplast, or kinetoplast DNA (kDNA), forms a dense, network-like mass within a single large mitochondrion and lies near the base of the flagellum where it is connected to the cell’s cytoskeleton by a specialized structure.

The kDNA network comprises two classes of circular DNA molecules: thousands of minicircles, typically about 0.5 to 2 kilobases in length, and a smaller number of maxicircles, roughly 20 to 40 kilobases long. Minicircles primarily encode transient RNA components known as guide RNAs, which direct RNA editing. Maxicircles carry a conventional mitochondrial gene set, including some components of the electron transport chain and rRNAs, but many of their transcripts are extensively edited after transcription.

RNA editing in kinetoplastids is a hallmark of kDNA function. Most mitochondrial mRNAs require uridine insertion and deletion guided by the gRNAs encoded on minicircles to produce translatable or functional transcripts. This extensive post-transcriptional processing links kDNA organization to mitochondrial gene expression and energy metabolism in these organisms.

Replication and segregation of the kDNA are tightly coordinated with the cell cycle. Minicircles periodically detach from the network, replicate as free circles, and reattach, a process coupled to the division of the single mitochondrion and the basal body–associated tripartite attachment complex. Because kDNA is essential for viability, its replication and RNA editing pathways are of interest as potential targets for antiparasitic interventions.