Sequence diversity in the kinetoplast DNA minicircles of Trypanosoma cruzi.

Minicircles are the most abundant component of the mitochondrially located kinetoplast DNA in the members of the order Kinetoplastida. Minicircle sequences differ among most trypanosomatid species. To learn about the molecular mechanisms that give rise to this diversity, we sequenced a complete minicircle (pTckAWP-2) and two homologous but polymorphic minicircle fragments isolated from different Trypanosoma cruzi clones. Comparison of these sequences revealed 23 point mutations, 19 of which were transitions. A single base pair insertion was also detected in one of the two minicircle fragments sequenced. Analysis of pTckAWP-2 sequence showed the following features: the presence of four internal 118 base pairs conserved regions with 80% or higher homology; the fact that these four conserved regions also differed mainly by point mutations, although in this case a bias in favor of transversions was observed; the existence in each of these four regions of the highly conserved 13 bp sequence 5'GGGGTTGGTGTAA3', detected in all trypanosomatid minicircles, which is thought to be the origin of replication; and the presence of several direct and inverted repeat sequences of 8 base pairs or longer, scattered throughout the minicircle molecule. Comparison of the T. cruzi conserved minicircle region with that of other trypanosomatids showed a higher homology of T. cruzi with T. lewisi, another stercorarian trypanosome, than with African trypanosomes or Leishmania.