Cloning of telomere-associated DNA using single-specific-primer polymerasechain reaction provides evidence for a conserved sequence directly adjacent to Theileria parva telomeric repeats

Telomere-associated (TA) DNA sequences of the intracellular protozoan paras ite Theileria parva were isolated by a novel strategy using a modified vers ion of single-specific-primer polymerase chain reaction (SSP-PCR). Nucleoti de sequences of noncoding TA DNA from three telomeres (6017 bp, 2435 bp and 4859 bp) contained no extensive tracts of repetitive DNA. Long open readin g frames (ORFs) were present at the centromeric ends of two of the TA seque nces, the 3' ends of the closest ORFs being only 2670 bp and 2719 bp from t he telomeric repeats. There were regions of significant similarity between the nucleotide sequences of the non-coding regions of different telomeres. The longest region of similarity was a virtually identical 1650 bp domain, located directly adjacent to the telomeric repeats of two separate telomere s. Comparison of the telomere proximal sequences defined in this study and two additional T. parva telomeres, whose sequences were determined previous ly, resulted in identification of a single copy 141 bp conserved sequence d irectly adjacent to the telomeric repeats. The conserved sequence is presen t at all five T. parva telomeres that have been characterised. The only org anism currently known to have a single copy conserved sequence located adja cent to the telomeric repeats is another intracellular protozoan, Leishmani a braziliensis. (C) 2000 Elsevier Science B.V. All rights reserved.