ANALYSIS OF MIXED PARASITE POPULATIONS OF THEILERIA-SERGENTI USING CDNA PROBES ENCODING A MAJOR PIROPLASM SURFACE PROTEIN

The gene for the 32 kDa surface protein (p32) of Theileria sergenti wa s cloned into lambda gt11 and its nucleotide sequence was determined. The gene encodes a protein of 283 amino acids as deduced from its nucl eotide sequence with a 22 residue N-terminal signal peptide. Using thi s cDNA as a probe we have isolated another two clones from a cDNA libr ary with a CDM8 vector system derived from the same parasite stock. Co mparison with three cDNA clones revealed differential polyadenylation and differences in sequences of non-coding regions. Within the coding regions, there were nucleotide transitions which affected the Pst I-re striction site, and one of the transitions was also accompanied by an amino acid substitution (Ala to Gly). Southern blot analysis showed hy bridization pattern changes among the parasites isolated from individu al calves at different times after infection. From these results, we c onclude that at least 3 genetically different parasite populations may coexist, and that transition to predominant parasite populations migh t occur during persistent infections in a host, possibly to evade the host immune responses.