A TFIIH-associated mediator head is a basal factor of small nuclear spliced leader RNA gene transcription in early-diverged trypanosomes.
Genome annotation suggested that early-diverged kinetoplastids possess a reduced set of basal transcription factors. More recent work, however, on the lethal parasite Trypanosoma brucei identified extremely divergent orthologs of TBP, TFIIA, TFIIB, and TFIIH which, together with the small nuclear RNA-activating protein complex, form a transcription preinitiation complex (PIC) at the spliced leader (SL) RNA gene (SLRNA) promoter. The SL RNA is a small nuclear RNA and a trans splicing substrate for the maturation of all pre-mRNAs which is metabolized continuously to sustain gene expression. Here, we identified and biochemically characterized a novel TFIIH-associated protein complex in T. brucei (Med-T) consisting of nine subunits whose amino acid sequences are conserved only among kinetoplastid organisms. Functional analyses in vivo and in vitro demonstrated that the complex is essential for cell viability, SLRNA transcription, and PIC integrity. Molecular structure analysis of purified Med-T and Med-T/TFIIH complexes by electron microscopy revealed that Med-T corresponds to the mediator head module of higher eukaryotes. These data therefore show that mediator is a basal factor for small nuclear SL RNA gene transcription in trypanosomes and that the basal transcription function of mediator head is a characteristic feature of eukaryotes which developed early in their evolution.
Lee
Ju Huck
JH
Department of Genetics and Developmental Biology, University of Connecticut Health Center, 400 Farmington Avenue, Farmington, CT 06030-6403, USA.
Cai
Gang
G
Panigrahi
Aswini K
AK
Dunham-Ems
Star
S
Nguyen
Tu N
TN
Radolf
Justin D
JD
Asturias
Francisco J
FJ
Günzl
Arthur
A
D001483:Base Sequence; D017931:DNA Primers / Q000235:genetics; D019143:Evolution, Molecular; D017125:Genes, Protozoan; D046529:Microscopy, Electron, Transmission; D008958:Models, Molecular; D046912:Multiprotein Complexes / Q000737:chemistry / Q000235:genetics / Q000648:ultrastructure; D011401:Promoter Regions, Genetic; D021122:Protein Subunits; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics* / Q000648:ultrastructure; D016053:RNA, Protozoan / Q000235:genetics*; D012342:RNA, Small Nuclear / Q000235:genetics*; D020038:RNA, Spliced Leader / Q000235:genetics*; D051758:Transcription Factor TFIIH / Q000737:chemistry / Q000235:genetics* / Q000648:ultrastructure; D014158:Transcription, Genetic; D014346:Trypanosoma brucei brucei / Q000235:genetics*
D017931:DNA Primers; D046912:Multiprotein Complexes; D021122:Protein Subunits; D015800:Protozoan Proteins; D016053:RNA, Protozoan; D012342:RNA, Small Nuclear; D020038:RNA, Spliced Leader; D051758:Transcription Factor TFIIH