Discussion

Gene expression control in Trypanosoma brucei is predominantly posttranscriptional and can be exerted on many levels, ranging from the efficiency of trans-splicing and polyadenylation, regulation of mRNA export, localisation and stability to translational efficiency and finally protein modification and stability. RNA-binding proteins are key players in regulating several of these aspects of gene expression control and thus play particularly important roles in the parasite. But is this also true for regulation of gene expression during the cell cycle? In the insect trypanosomatid Crithidia fasciculata a cycling sequence binding protein complex II (CSBPII) has been identified. CSBPII consist of the RNA-binding proteins RBP33, RBP45 and a poly(A) binding protein and has been reported to regulate expression of S-phase transcripts. These transcripts share a common hexamer motif in their untranslated regions important for CSBPII binding. We wondered if the homologous TbRBP33 and TbRBP45 play a similar role in cell cycle dependent mRNA regulation in T. brucei. Hence we investigated expression of these two RBPs and their potential targets during the trypanosome cell cycle, assayed their essentiality using RNAi and attempted to identify interaction partners by immunoprecipitation. Results of these experiments will be presented.