A TFIIB-like protein is indispensable for spliced leader RNA gene transcription in Trypanosoma brucei

The lack of general class II transcription factors was a hallmark of the genomic sequences of the human parasites Trypanosoma brucei, Trypanosoma cruzi and Leishmania major. However, the recent identification of TFIIA as part of a protein complex essential for RNA polymerase II-mediated transcription of SLRNA genes, which encode the trans splicing-specific spliced leader RNA, suggests that trypanosomatids assemble a highly divergent set of these factors at the SLRNA promoter. Here we report the identification of a trypanosomatid TFIIB-like (TFIIBlike) protein which has limited overall sequence homology to eukaryotic TFIIB and archaeal TFB but harbors conserved residues within the N-terminal zinc ribbon domain, the B finger and cyclin repeat I. In accordance with the function of TFIIB, T.brucei TFIIBlike is encoded by an essential gene, localizes to the nucleus, specifically binds to the SLRNA promoter, interacts with RNA polymerase II, and is absolutely required for SLRNA transcription.