Kinetoplast DNAs (kDNA) are the most startlingly complex and unexpected DNA structures anywhere. Superlatives do not suffice, as you will see. kDNAs are found only in the kinetoplast of flagellates, structures involved in chromosome segregation, which is probably the reason why they may not be as well known as they deserve. In these organisms, mitochondrial DNA is called kinetoplast DNA and consists of a network of thousands of interlocked (catenated) circles that come in two sizes, maxi- (typically 20 ‒ 40 kb) and mini-circles (0.5 ‒ 1.0 kb). Usually, maxis are present in only a few dozen per network, minis in the thousands. To paraphrase a terrific review by Jensen and Eglund what do they do? "Maxicircles, like mitochondrial DNAs from more conventional organisms, encode rRNAs and several proteins involved in energy transduction (including subunits of cytochrome oxidase, NADH dehydrogenase, and the ATP synthase). Maxicircle transcripts in T. brucei are heavily edited, an amazing reaction in which uridylate residues are incorporated into or removed from specific internal sites within the transcript to create an open reading frame. Minicircles encode most of the small guide RNAs that are templates for editing specificity. Because the mitochondrial transcripts in T. brucei contain so many editing sites, they require many different guide RNAs to produce a set of functional mRNAs. Thus, the minicircle population is large and heterogeneous, with different DNA species encoding different guide RNAs. C. fasciculata minicircles are less complex, with one predominant minicircle class."