Characterization of a polymorphic gene of T. lestoquardi and of a recently identified Theileria species pathogenic for small ruminants in China.

In the present study, we identified a gene from Theileria lestoquardi and from a recently described Theileria species which is highly pathogenic for small ruminants in China. Since the taxonomic position of the latter parasite is still not clear, we refer to it as Theileria (China) species. The gene described here comprises an open reading frame of about 948 bp which prospectively encodes a 35-kDa protein. Its sequence is most closely related to the polymorphic immunodominant membrane protein of T. parva (36% identity). A search for sequence patterns and motifs within the predicted amino acid sequence revealed that this gene possesses three membrane-spanning regions at its C-terminal part, suggesting that it is a membrane protein. Several allelic variants of this gene were found in each parasite species, demonstrating interspecies and intraspecies variation. The predicted amino acid sequence variants display a substantial size and sequence polymorphism in the central part of its presumed extracellular region, while the N-terminal and the transmembrane/intracellular regions are highly conserved.