NOVEL PATTERN OF EDITING REGIONS IN MITOCHONDRIAL TRANSCRIPTS OF THE CRYPTOBIID TRYPANOPLASMA-BORRELI

In mitochondria of Kinetoplastida belonging to the suborder Trypanosom atina, the nucleotide sequence of transcripts is post-transcriptionall y edited via insertion and deletion of uridylate residues. In order to shed more light on the evolutionary history of this process we have s earched for editing in mitochondrial RNAs of Trypanoplasma borreli, an organism belonging to the suborder Bodonina. We have cloned and seque nced a 5.3 kb fragment derived from a 37 kb mitochondrial DNA molecule which does not appear to be a part of a network structure and have fo und genes encoding cytochrome c oxidase (cox) subunit 1, cox 2 and apo cytochrome (cyt) b, and genes encoding the small and large subunit mit oribosomal RNAs. The order in which these genes occur is completely di fferent from that of trypanosomatid maxicircle genes. The 5' and 3' te rmini of both the cytb and cox1 gene are cryptic, the protein coding s equences being created by extensive insertion/deletion of Us in the co rresponding mRNA sections. Phylogenetic analyses of the protein and ri bosomal RNA sequences demonstrated that the separation between T.borre li and Trypanosomatina was an early event, implying that U-insertion/d eletion processes are ancient. Different patterns of editing have pers isted in different lineages, however, since editing of cox1 RNA and of relatively small 3'-terminal RNA sections is not found in trypanosoma tids. In contrast, cox2 RNA which is edited in trypanosomatids by the insertion of four Us, is unedited in T.borreli.