The ves multigene family of B-bovis encodes components of rapid antigenic variation at the infected erythrocyte surface

B. bovis, an intraerythrocytic protozoal parasite, establishes chronic infe ctions in cattle in part through rapid variation of the polymorphic, hetero dimeric VESA1 protein on the infected erythrocyte surface and sequestration of mature parasites. We describe the characterization of the ves1 alpha ge ne encoding the VESA1a subunit, thus providing a description of a gene whos e product is involved in rapid antigenic variation in a babesial parasite. This three-exon gene, a member of a multigene family (ves), encodes a polyp eptide with no cleavable signal sequence, a single predicted transmembrane segment, and a cysteine/lysine-rich domain. Variation appears to involve cr eation and modification or loss of a novel, transcribed copy of the gene.