Oligonucleotide probes complementary to variable regions of 18S rRNA from Sarcocystis species.

Sarcocystis is a large genus of cyst-forming coccidian parasites in the phylum Apicomplexa (Protista). Stable RNA was extracted from cystozoites of Sarcocystis cruzi, S. tenella, S. fusiformis, S. gigantea and Toxoplasma gondii. The partial sequences of the small sub-unit ribosomal RNA (18S rRNA) were determined by direct RNA sequencing with reverse transcriptase. The rRNA sequences were computer aligned with the published partial sequence of T. gondii, and three oligonucleotides complementary to different variable regions of the 18S rRNA were synthesized. The three probes were end-labelled with 32P and tested in filter hybridization experiments. One of the probes designed to be Sarcocystis genus-specific, did not cross-hybridize to stable RNA from T. gondii. Two of the probes were designed to be species-specific for S. cruzi and S. tenella, and these probes hybridized specifically with their respective targets.