In the pathogenic trypanosome, Trypanosoma brucei, transcription factor IIB (tTFIIB) is essential for spliced leader (SL) RNA gene transcription and cell viability, but has a highly divergent primary sequence in comparison to TFIIB in other eukaryotes. Structure analysis of the C-terminal region of trypanosome TFIIB, reveals 2, closely packed helical modules followed by a C-terminal extension of 32 aa. The trypanosome-specific region comprises the second helical module and the C-terminal extension. Both helical modules contain the canonical 5-helix cyclin fold characteristic of TFIIB proteins [1]. This domain is mostly found in Trypanosomatidae.

1: Structure of the C-terminal domain of transcription factor IIB from Trypanosoma brucei. Ibrahim BS, Kanneganti N, Rieckhof GE, Das A, Laurents DV, Palenchar JB, Bellofatto V, Wah DA; Proc Natl Acad Sci U S A. 2009;106:13242-13247. PMID:19666603