Abstract
Protein-coding genes of trypanosomes are mainly transcribed polycistronically and cleaved into functional mRNAs in a process that requires
trans
splicing of a capped 39-nucleotide RNA derived from a short transcript, the spliced-leader (SL) RNA. SL RNA genes are individually transcribed from the only identified trypanosome RNA polymerase II promoter. We have purified and characterized a sequence-specific SL RNA promoter-binding complex, tSNAP
c
, from the pathogenic parasite
Trypanosoma brucei
, which induces robust transcriptional activity within the SL RNA gene. Two tSNAP
c
subunits resemble essential components of the metazoan transcription factor SNAP
c
, which directs small nuclear RNA transcription. A third subunit is unrelated to any eukaryotic protein and identifies tSNAP
c
as a unique trypanosomal transcription factor. Intriguingly, the unusual trypanosome TATA-binding protein (TBP) tightly associates with tSNAPc and is essential for SL RNA gene transcription. These findings provide the first view of the architecture of a transcriptional complex that assembles at an RNA polymerase II-dependent gene promoter in a highly divergent eukaryote.