Identification and characterization of two trypanosome TFIIS proteins exhibiting particular domain architectures and differential nuclear localizations.

Nuclear transcription of Trypanosoma brucei displays unusual features. Most protein-coding genes are organized in large directional gene clusters, which are transcribed polycistronically by RNA polymerase II (pol II) with subsequent processing to generate mature mRNA. Here, we describe the identification and characterization of two trypanosome homologues of transcription elongation factor TFIIS (TbTFIIS1 and TbTFIIS2-1). TFIIS has been shown to aid transcription elongation by relieving arrested pol II. Our phylogenetic analysis demonstrated the existence of four independent TFIIS expansions across eukaryotes. While TbTFIIS1 contains only the canonical domains II and III, the N-terminus of TbTFIIS2-1 contains a PWWP domain and a domain I. TbTFIIS1 and TbTFIIS2-1 are expressed in procyclic and bloodstream form cells and localize to the nucleus in similar, but distinct, punctate patterns throughout the cell cycle. Neither TFIIS protein was enriched in the major pol II sites of spliced-leader RNA transcription. Single RNA interference (RNAi)-mediated knock-down and knockout showed that neither protein is essential. Double knock-down, however, impaired growth. Repetitive failure to generate a double knockout of TbTFIIS1 and TbTFIIS2-1 strongly suggests synthetical lethality and thus an essential function shared by the two proteins in trypanosome growth.