Abstract: 【Abstract】 Objective To study the TaSP polymorphism in three Chinese isolates of Theileria annulata. Methods The isolates from Inner Mongolia Autonomous Region， Ningxia Hui Autonomous Region and Xinjiang Uygur Autonomous Region were cultured in RPMI 1640 medium. TaSP gene was amplified from genomic DNA extracted from schizonts using polymerase chain reaction （PCR） and sequenced. Its amino acid sequence comparison was carried out with Clustal W2 multiple sequence alignment program. Molecular component and motif prediction were performed with online servers. Results The comparison of TaSP amino acid sequences of the three isolates showed that the central region （aa position 38-161） predicted to be the highly immunogenetic domain was polymorphic both in size and amino acid sequence， while the N-terminal （first 37 aa） and C-terminal （last 154 aa） parts were strongly conserved. Phylogenetic analysis and percentage identity revealed that the Chinese isolates were closely related to the isolates from Turkey， but quite different from those of India， Morocco and Tunisia. More importantly， variability was noticed among Chinese isolates， which caused both the location and number′s differences of motif （casein kinase II phosphorylation sites） among three TaSP sequences. Conclusion TaSP polymorphism exists in the Chinese isolates of T. annulata.

Key words: Theileria annulata, TaSP, Chinese isolate, Sequence analysis, Polymorphism