Characterization of the Unusual Bidirectional ves Promoters Driving VESA1 Expression and Associated with Antigenic Variation in Babesia bovis

Rapid clonal antigenic variation inBabesia bovis involves thev ariante rythrocytes urfacea ntigen-1 (VESA1) protein expressed on the infected-erythrocyte surface. Because of the significance of this heterodimeric protein for demonstrated mechanisms of parasite survival and virulence, there is a need to understand how expression of theves multigene family encoding this protein is controlled. As an initial step toward this goal, we present here initial characterization of theves promoter driving transcription of VESA1a and -1b subunits. A series of transfection constructs containing various sequence elements from thein vivo locus of activeves transcription (LAT) were used to drive expression of the firefly luciferase gene in a dual luciferase-normalized assay. The results of this approach reveal the presence of two bidirectional promoter activities within the 434-bp intergenic region (IGr), influenced by putative regulatory sequences embedded within the flankingves 1α andves 1β genes. Repressor-like effects on the apposing gene were observed for intron 1 of bothves 1α andves 1β. This effect is apparently not dependent upon intronic promoter activity and acts only incis . The expression of genes within theves family is likely modulated by local elements embedded withinves coding sequences outside the intergenic promoter region in concert with chromatin modifications. These results provide a framework to help us begin to understand gene regulation during antigenic variation inB. bovis .