Generation of a mosaic pattern of diversity in the major merozoite-piroplasm surface antigen of Theileria annulata

The polypeptide Tams1 is an immunodominant major merozoite piroplasm surfac e antigen of the protozoan parasite Theileria annulata. Generation and sele ction of divergent antigenic types has implications for the inclusion of th e Tams1 antigen in a subunit recombinant vaccine or use in the development of a diagnostic ELISA. In this study a total of 129 Tams1 sequences from pa rasites isolated in Bahrain, India, Italy, Mauritania, Portugal, Spain, Sud an, Tunisia and Turkey were obtained to estimate the extent of Tams1 divers ity throughout a wide geographical range, Significant sequence diversity wa s found both within and between isolates and many of the sequences were uni que. No geographical specificity of sequence types was observed and almost identical sequences occurred in different geographical areas and a panmicti c population structure is suggested by our results. A sliding window analys is identified sub-regions of the molecule where selection for amino acid ch anges may operate. Evidence is also presented for the generation of diversi ty through intragenic recombination with switching of corresponding variabl e domains between alleles. Recombination to exchange variable domains appea rs to occur throughout the length of the gene sequence, and has the potenti al to generate a mosaic pattern of diversity. (C) 2000 Elsevier Science B.V . All rights reserved.