Transcription of kinetoplast DNA minicircles.

The mitochondrial DNA of trypanosomes is organized as a network of catenated circular DNA molecules called the kinetoplast. The minicircles of the kinetoplast are 1 kb circular DNA molecules present at 5,000-10,000 copies per network. The maxicircles are 20 kb circular molecules present at 50-100 copies per network. Maxicircles are transcribed and are thus analogous to mitochondrial DNAs. Here we show that, contrary to previous reports, the minicircles of T. brucei are also transcribed. A minicircle transcript of approximately 240 nucleotides is present in bloodstream and insect developmental stages of the parasite, is enriched in purified mitochondrial preparations, and is efficiently synthesized in vitro. The minicircle cDNA overlaps the conserved region of the T. brucei minicircle and is juxtaposed to a 12 base sequence common to all minicircles. These findings indicate that minicircles, in addition to their previously proposed structural role, are transcribed.