Unusual Features of Kinetoplast DNA from Trypanosomes: Novel Mechanism of Gene Expression (RNA-Editing), The Absence of tRNA Genes and the Variable Presence of a Cytochrome Oxidase Subunit Gene

Abstract

Kinetoplast DNA is the unorthodox mitochondrial (mt)DNA of Trypanosomes which consists of a network of catenated circular DNAs of two types: about 10⁴ minicircles (1–3 kb, depending on the species) and 25–50 maxicircles (20–40 kb). The coding capacity of this mtDNA resides in the maxicircle component. The nucleotide sequences of large portions of the maxicircles of Trypanosoma brucei, Crithidia fasciculata and Leishmania tarentolae have been determined. So far, genes coding for mitochondrial rRNAs, apocytochrome b, cytochrome oxidase subunits (cox) I, II and III (present in C. fasciculata and L. tarentolae but absent in T. brucei), NADH dehydrogenase subunits (ND) I, IV and V and some unassigned reading frames (URF) have been identified (reviewed in 1). A comparison of trypanosomal mitochondrial genes with those of other organisms reveals a wealth of unusual features not only with respect to the genes themselves, but also to the way they are organized and expressed. Four of these unusual aspects will be discussed.