Authors

A Saura³; D López-Farfán³; P Iribarren²; V Alvarez²; I Vidal³; J M Bart³; M Field¹; M Navarro³;  ¹ Biological Chemistry and Drug Discovery, School of Life Sciences, University of Dundee;  ² IIB-INTECH, Argentina;  ³ Instituto de Parasitologia y Biomedicina "Lopez-Neyra", CSIC. Granada, Spain

Discussion

Post transcriptional modification by the Small Ubiquitin MOdifier (SUMO) peptide functions in Variant Surface Glycoprotein (VSG) expression in Trypanosoma brucei. SUMO-conjugated nuclear proteins are enriched in the High SUMOylated Focus (HSF) that partially colocalizes with the Expression Site Body (ESB), the nuclear body where VSG is transcribed. Proteomic analyses of HA-SUMO-conjugated proteins identified Transcription Activator 1 (TAF1), a SNF2 family member. Functional characterization of TAF1 by RNAi showed a significant reduction (50%) of active VSG221 mRNA levels. ChIP analysis showed RNA Polymerase I occupancy decreased on the active VSG221 following TAF1 KD, suggesting this factor is required for VSG transcription. TAF1-ChiP analysis suggested occupancy at sequences upstream of the VSG promoter. DNAs isolated from TAF1 ChIP experiments showed heterogeneity of the VSG promoter sequences suggesting TAF1 is located not only in the active VSG221, but rather in many other inactive ones. Upon TAF1 KD, we also detected an unexpected increase of Procyclin mRNA, normally repressed in the bloodstream form. Thus, we investigated Protein Associated with Differentiation (PAD1 and PAD2) expression levels. TAF1 KD showed a clear upregulation of PADs, suggesting TAF1 also regulates differentiation. Together these data suggest a dual function of TAF1 that regulates both, VSG transcription and developmentally regulated gene expression.