TaCRK3 encodes a novel Theileria annulata protein kinase with motifs characteristic of the family of eukaryotic cyclin dependent kinases: A comparative analysis of its expression with TaCRK2 during the parasite life cycle

The TaCRK3 gene from the bovine apicomplexan parasite Theileria annulata, encodes a 46 kDa polypeptide with strong homology to the eukaryotic family of cyclin-dependent kinases. TaCRK3 does not show significant alignment with any particular CDK group, other than the Pfmrk kinases from the related apicomplexans Plasmodium falciparum and Plasmodium yoelii. It has a putative bipartite nuclear localization signal and is located to parasite nuclei by IFAT. Protein levels are constitutive throughout differentiation of the intra-lymphocytic macroschizont. This contrasts with the expression pattern of TaCRK2 (Kinnaird et al., 1996. Mol. Microbiol., 22, 293-302) which is closely related to the eukaryotic CDK1 /2 families involved in regulation of cell cycle progression. TaCRK2 is also located to the parasite nuclei but has no nuclear localization signal and exhibits transient up-regulation in protein levels during mid-merogony. However compared to TaCRK3, it shows down-regulation near the end of merogony. We predict that TaCRK3 may have a role in regulation of gene transcription while TaCRK2 is more likely to be involved in control of parasite nuclear division.