Theileria parva is an obligate intracellular protozoan parasite which is the causative agent of East Coast fever, an acute, leukemia-like disease of cattle. The intralymphocytic stage of the parasite induces blastogenesis and clonal expansion of quiescent bovid lymphocytes. Experiments in our laboratory have shown a marked increase of casein kinase II- (CK II-) like activity in T. parva-transformed lymphocytes. We have also detected CK II activity in purified T. parva schizonts. To explore the significance of this increase, we used a Drosophila melanogaster CK II alpha cDNA probe [Saxena et al. (1987) Mol. Cell Biol. 7, 3409-3417] to isolate a T. parva genomic clone encoding a CK II catalytic subunit. The clone contains a 1.3-kb open reading frame coding for a predicted protein of 420 amino acids (M(r) 50,200). Northern blot analysis revealed a single transcript of 1.65 kb. The deduced T. parva CK II catalytic subunit sequence shows, over 321 residues comprising the C-terminus of the molecule, extensive identity with CK II alpha and alpha' sequences from both vertebrate and invertebrate organisms. The T. parva CK II subunit amino acid sequence displays 68% identity with the Drosophila alpha subunit and 67% with the Caenorhabditis elegans alpha subunit but only 58% and 56% sequence identity with the Saccharomyces cerevisiae alpha and alpha' subunits, respectively. Comparison of the T. parva sequence with higher eukaryotic alpha and alpha' sequences reveals that it is most identical with the alpha subunit. A unique component of the T. parva CK II alpha subunit is a 99 amino acid sequence at the N-terminus, which contains a sequence motif with features characteristic of signal peptides.