Practice question

In mitochondria of trypanosomatids including Trypanosoma brucei, many protein-coding genes exist as cryptogenes requiring extensive uridine insertion and deletion editing guided by small noncoding guide RNAs encoded in kinetoplast DNA. Guide RNAs form short anchor duplex with pre-messenger RNA upstream of editing sites, specifying positions via base pairing where editosome complex containing endonuclease, 3' terminal uridylyltransferase TUTase adding uridines, and RNA ligase executes insertions. Editing can add hundreds of uridines and delete dozens, dramatically remodeling open reading frames to generate functional cytochrome oxidase subunits and other mitochondrial proteins essential for respiration.