Antigenic Switching by VSG Gene Conversion in T. brucei

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DESCRIPTION (provided by the applicant): Trypanosoma brucei is a eukaryotic parasite that evades mammalian host immune response by antigenic variation: changing its Variant Surface Glycoprotein (vsG) ?coat? by alternatively expressing one among hundreds of highly diverged VSG genes in its genome Most VSG switches occur by the little-studied process of gene conversion. Here, a new strategy is proposed, replacing VSG ORFs with selectable markers, to investigate parameters affecting gene conversion of VSG cassettes. Drug selection will detect recombination of promoter-less markers with the active VSG, allowing isolation and study of rare gene conversion events. The hypothesis that recombination rates differ for internal versus telomeric VSGS will be evaluated by measuring gene conversion from markers placed at each type of site. Creating lines with latent promoters upstream of silent telomeric VSGs will detect otherwise ?silent? switches, which might shuffle and increase the availability of VSGS at ?preferred? chromosornal locations. The reporter constructs can be altered to test the role of conserved sequence motifs of VSG gene conversion cassettes for effects on the rates and order of VSG switching. The influence of chromosomal context and local sequence elements on recombination will be teased apart. A thorough understanding of VSG gene conversion will allow development of more accurate models to explain and predict patterns of antigenic variation. This work is highly relevant to host-pathogen interactions, especially in trypanosomes and malaria parasites.