AN ORGANELLE-LIKE SMALL-SUBUNIT RIBOSOMAL-RNA GENE FROM BABESIA-BOVIS - NUCLEOTIDE-SEQUENCE, SECONDARY STRUCTURE OF THE TRANSCRIPT AND PRELIMINARY PHYLOGENETIC ANALYSIS

Investigations aimed at identifying the mitochondrial genome of Babesia Bovis using the polymerase chain reaction (PCR) have established the existence of an organelle-like small subunit ribosomal RNA (SSU rRNA) gene in the parasite. The sequence, compiled from three main PCR products, was 1448 bp in length (including the primer regions), had a 73% A+T content and showed significant similarity (68% sequence identity) to the ''organellar'' SSU rRNA gene from Plasmodium falciparum. The proposed secondary structure of the transcript showed several features which were consistent with a eubacterial origin for the organelle-like gene. The presence of putative binding sites for streptomycin and tetracycline also supported an ''organellar'' location for the gene and suggested that the SSU rRNA transcript is functional in protein synthesis because tetracycline has anti-babesial activity. Phylogenetic analyses based on the conserved regions of the SSU-like rRNA genes from a wide variety of organisms showed only a weak association of the babesial sequence with its mitochondrial homologues and an even weaker association with the corresponding genes of plastid origin. The origin of this organelle-like gene in B. bovis therefore remains unresolved, as is the ease for its homologue from P. falciparum.