Transcription map of the Trypanosoma brucei mitochondrial genome.

In trypanosomes belonging to the order Kinetoplastida the mitochondrial DNA consits of an immens complex of concatenated minicircles (10 000) and some 50 maxicircles. The latter is the equivalent of the classical mitochondrial genome of other organisms and contains a number of genes coding for some of the components of the mitochondrial respiratory chain. Many of these genes are however incomplete and require editing of their transcribed RNA in order to give rise to a functional protein product. Editing is carried out with the help of a great number of guide RNAs, which are encoded by the many slightly different minicircles.

Linear map of the 22-kb maxicircle of T. brucei. The genes above the line are transcribed from left to right, whereas the genes beneath the line are transcribed from the right to the left. The 9S and 12S rRNA genes have added uridines at their 3' termini (black boxes). Transcripts from Cyb, COII and MURF2 have limited internal editing (black boxes). Shaded boxes indicate genes that are extensively or pan-edited. The variable region of the maxicircle is indicated by VR.

See more details on RNA editing on Larry Simpsons RNA editing site

Diffferent types of RNA editing*

Type	Organism	Transcript (Genome)	Cis-acting Elements	Trans-acting factors	Mechanism
U Insertion/deletion	Kinetoplastids	mRNA (mt)	Anchoring sequences	gRNAs,TUTase, RNA ligase, endonuclease, other factors	cleavage ligation or trsansesterification
Mostly C insertion, also U, AA, CU, GU, GC	Physarum polycaephalum	mRNA, rRNA, tRNA (mt)	?	?	?
3' terminal A addition	vertebrates	mRNA (mt)	flanking tRNA structures	Endonuclease, TATase	cleavage/TATase action

*From: Gert-Jan Arts, RNA editing in Kinetoplastida, PhD Thesis, 1995,
University of Amsterdam

Last updated: 3 September 1997.