Trypanosoma brucei is a protist parasite of Sub-Saharan Africa causing Sleeping Sickness in humans and Nagana in various livestock. 60 million people are at risk to be infected, there are an estimated 500,000 cases each year, and in some provinces, African trypanosomiasis has a prevalence of 50%. Untreated, the disease is fatal. However, existing drugs are very toxic, too expensive, and/or not effective against all subspecies of the parasite. Moreover, resistance to existing drugs is on the rise and vaccine development not in sight. Thus, identification of novel drug targets is a primary goal. T. brucei lives freely in the blood of its mammalian host and is transmitted by its tsetse vector (Glossina). Trypanosome survival inside the hosts depends on a dense glycoprotein coat covering the parasite's cell surface and protecting it from lytic host components. Moreover, antigenic variation of the coat is the means by which the parasite evades the mammalian immune system. The coat consists of procyclin in the insect form or of a single type of variant surface glycoprotein in the bloodstream form. The genes encoding these essential proteins are transcribed by RNA polymerase I. This is unique, because in eukaryotes RNA polymerase I exclusively transcribes ribosomal DNA and all mRNA is synthesized by RNA polymerase II. Furthermore, T. brucei deviates from standard eukaryotic gene expression by transcribing its genes in a polycistronic fashion. Individual mRNAs are processed from large precursors by spliced leader (SL) trans splicing and polyadenylation. Since trans splicing is an essential maturation step for all mRNA, parasite growth crucially depends on a strong and continuous supply of SL RNA, the SL donor molecule. Our research focuses on both RNA pol I-mediated transcription of genes encoding the major cell surface proteins and synthesis of SL RNA. It is directed towards the identification and functional characterization of transcription factors (or factor domains) which are essential for the parasite and absent in the host. For functional analysis, we have developed an in vitro transcription system. Other key experimental strategies include genetic analysis of transcription determinants, tandem affinity purification of transcription complexes, and in vivo analysis of factors by conditional RNA interference.