Cloning and characterisation of cDNA clones encoding two Babesia bovis proteins with homologous amino- and carboxy-terminal domains.

A dextran sulphate protein (DSP) fraction derived from Babesia bovis has previously been shown to induce a protective immune response in cattle. A B. bovis cDNA library was screened with both the complete anti-DSP serum and a subfraction of the anti-DSP serum affinity purified on a native B. bovis protein of approx. 80 kDa. cDNA clones encoding two different B. bovis proteins were identified. The product of one gene, Bv80, has a single divergent copy of a sequence of 149 amino acids (approx. 30% amino acid identity) in both the amino- and carboxy-terminal domains. These domains are separated by an array of short variant repeat sequences rich in proline and glutamic acid. The product of the other gene, BvVAl (homologous to the previously described 225-kDa B. bovis protein)[19], is predicted to have a single divergent copy of a sequence of 170-171 amino acids (approx. 35% amino acid identity) in both the amino- and carboxy-terminal domains. These domains are also separated by an array of repeats. The 73-amino acid repeat unit of this array is composed of a number of variant derivatives of shorter repeat units. Detailed analysis of genomic clones flanking two alleles of the gene encoding BvVAl/225 kDa identified further members of a multi-gene family. This region of the genome of B. bovis has been subject to a large number of amplification processes.