maxicircle

Maxicircle is a class of circular DNA molecules found in the kinetoplast of kinetoplastid protozoa, such as Trypanosoma and Leishmania. It forms part of the kinetoplast DNA (kDNA) network, which also includes thousands of small minicircles. The maxicircle represents the mitochondrial genome portion with a more conventional gene content, while minicircles encode the necessary guide RNAs for RNA editing.

Maxicircles are typically about 20 to 30 kilobases in length and contain a subset of mitochondrial genes, including several components of the electron transport chain, such as NADH dehydrogenase and cytochrome oxidase subunits, and sometimes ribosomal RNA genes. However, many maxicircle transcripts are not immediately functional and require extensive post-transcriptional RNA editing to produce translatable messages. This editing predominantly involves the insertion and deletion of uridines to restore proper reading frames.

RNA editing is guided by small RNA molecules encoded by the minicircles, known as guide RNAs (gRNAs). The gRNAs determine the specific edits needed for each maxicircle transcript, coordinating the production of functional mitochondrial proteins. The maxicircle and minicircle components persist together within a single mitochondrion and are maintained as a dynamic, interconnected network that undergoes coordinated replication and segregation during cell division.

Biological and research relevance: The maxicircle genome, together with the RNA editing system, is characteristic of kinetoplastids and provides useful markers for phylogenetic and taxonomic studies. Variation in maxicircle sequences among species and strains can aid in species identification and evolutionary analyses.