EVIDENCE FOR 2 SINGLE-COPY UNITS IN THEILERIA-PARVA RIBOSOMAL-RNA GENES

Bacteriophage clones containing ribosomal RNA genes of Theileria parva were isolated from genomic DNA libraries. Physical mapping studies re vealed 2 ribosomal DNA units, which were distinguishable by restrictio n enzyme site polymorphisms in flanking sequences. The cloned ribosoma l DNA units were mapped to 2 separate T. parva chromosomes. Analysis o f sequences contained in lambda EMBL3 recombinants, together with Sout hern blot analysis of genomic DNA and data on the copy number of the r RNA genes, suggested that the rDNA units were not tandemly repeated. T his organisation of ribosomal transcription units is similar to that d escribed for other genera of apicomplexan protozoa, but 2 rDNA units, each containing single copies of the rRNA coding genes, would be the l owest copy number described for any eukaryote in which amplification o f rRNA genes is not known to occur. EcoRI restriction fragment length polymorphisms, which were revealed using rRNA gene probes, separated T . parva stocks into 2 categories. Nucleotide sequence analysis of poly merase chain reaction-amplified internal transcribed spacer DNA reveal ed 2 different ITS sequences derived from rDNA transcription units wit hin the genome of a cloned T. parva parasite. Polymorphism was also ob served between ITS sequences amplified from the DNA of different T. pa rva stocks. A synthetic oligonucleotide derived from T. parva Uganda r ibosomal ITS DNA sequences hybridised to DNA from the T. parva Uganda stock, but not to the DNA of the T. parva Muguga stock. This oligonucl eotide is potentially useful as a marker for the T. parva Uganda stock .