A 7.1 kb linear DNA molecule of Theileria parva has scrambled rDNA sequences and open reading frames for mitochondrially encoded proteins.

Abstract

Theileria parva, an intralymphocytic protozoan parasite of cattle, contains a linear 7.1 kb DNA element with terminal inverted repeat sequences. The molecule is transcribed into low molecular weight RNA, and both DNA strands encode short stretches of unique sequences, usually < 100 nucleotides, which are similar to large (LSU) or small (SSU) ribosomal subunit RNA. Phylogenetically conserved conformational rRNA domains were assembled from the discontinuous rDNA sequences using comparative secondary structure modelling. For example, a minimum of four predicted sequences, two derived from each DNA strand, is required to assemble domain V of LSU rRNA which participates in peptidyl transferase activity. The discontinuities in the identified rRNA domains fall within regions of no known functional significance. Hence, it is likely that the element encodes fragmented rDNA genes and the mature rRNA is unconventional, consisting of several fragments of RNA, primarily held together by intermolecular and intramolecular base pairing. The element also has ORFs for components of the last two mitochondrial electron transport enzyme complexes. The structure of the parasite DNA element, its protein coding capacity and scrambled rDNA gene sequences, are reminiscent of the mitochondrial genome of Chlamydomonas reinhardtii. We propose that the 7.1 kb element is equivalent to the mitochondrial DNA of T. parva, although a number of its features are unusual for this family of extrachromosomal DNA molecules.

Expressed sequence tag (EST) analysis of the erythrocytic stages of Babesia bovis

“…Remarkably, this rRNA is encoded by a discontinuous gene which is scattered over both strands of the mitochondrial genome (Genbank Accession Nr. 2981472) like in P. falciparum (Feagin, 1992) and T. parva (Kairo et al, 1994). Short transcripts of these regions were observed in these species.…”

The evolution of primate malaria parasites based on the gene encoding cytochromebfrom the linear mitochondrial genome

“…Protein base alignments were performed for each of two additional Apicomplexa parasites that were used as outgroups: Toxoplasma gondii (GenBank accession no. AF023246 submitted by D. C. McFaden and J. C. Boothroyd, Stanford University, CA) and Theileria parva (30). These Apicomplexa parasites are considered distantly related to Plasmodium (7,31).…”

Extrachromosomal DNA in the Apicomplexa

“…Hall et al (50) reported the T. annulata version as a 6.5-kb multicopy sequence, which they initially supposed had a chromosomal origin, but correctly identified its mitochondrial provenance when they found it encoded a gene for cyt b (73). A more detailed study of the comparable element from T. parva (62) showed that it had essentially the same genetic content as the malarial version, although, as illustrated in Fig. 8, there are significant differences in gene order between the two genomes.…”