Background: Because of the strong immunologic responses of surface protein TaSp in Theileria annulata infected host, we tried to characterize this protein in a T. annulata isolate from Iran. Methods: The RNA prepared from T. annulata infected cells was used to produce SMART-DScDNA. The Double strand cDNA was then amplified with primers derived from TaSp mRNA sequences. The PCR product was cloned in pTZ57R/T vector, sequenced and registered under accession no. JQ003240 in GenBank. Results: The sequence analysis showed 90%-94% nucleotide sequence identity and 68%-94% amino acid homology to the corresponding sequences of TaSp gene by T. annulata, T. sp. china I, T. sp. China and T. lestoquardi and three T. annulata reported from Iran respectively. Interestingly, the sequence analysis also showed small nucleotide sequence region near the 5` end in which the presented TaSp protein differed very strongly from the other known TaSp sequences. For the preparation of the recombinant protein, the cDNA was cloned in pQE-32 vector, the recombinant protein was prepared and assayed by Theileria infected bovine serum. Conclusion: The polymorphism in TaSp gene could be detected in intra-as well as inter species. The different characterized TaSp proteins had a common identic region, which may be helpful for development of broad band vaccine based on the recombinant proteins. The polymorphism in this gene, make this protein also interesting for the diagnostic purposes.

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