Analysis of a donor gene region for a variant surface glycoprotein and itsexpression site in African trypanosomes

African trypanosomes evade the immune response of their mammalian hosts by sequentially expressing genes for different variant surface glycoproteins ( VSGs) from telomere-linked VSG expression sites. In the Trypanosoma brocei clone whose genome is being sequenced (GUTat 10.1), we show that the expres sed VSG(VSG 10.1) is duplicated from a silent donor VSG located at another telomere-linked site. We have determined two 130 kb sequences representing the VSG 10.1 donor and expression sites. The telomere-linked donor VSG 10.1 resembles metacyclic VSG expression sites, and is preceded by a cluster of 35 or more tandem housekeeping genes, all of which are transcribed away fr om the telomere. The 45 kb telomere-linked VSG 10.1 expression site contain s a promoter followed by seven expression site-associated genes (ESAGs), th ree pseudo ESAGs, two pseudo VSGs and VSG 10.1. The 80 kb preceding the exp ression site has few, if any, functional ORFs, but contains 50 bp repeats, INGI retrotransposon-like elements, and novel 4-12 kb repeats found near ot her telomeres. This analysis provides the first look over a 130 kb range of a telomere-linked donor VSG and its corresponding telomere-linked VSG expr ession site and forms the basis for studies on antigenic variation in the c ontext of a completely sequenced genome.