A novel transcription initiation factor (TIF), TIF-IE, is required for homogeneous Acanthamoeba castellanii TIF-IB (SL1) to form a committed complex.
The fundamental transcription initiation factor (TIF) for ribosomal RNA expression by eukaryotic RNA polymerase I, TIF-IB, has been purified to near homogeneity from Acanthamoeba castellanii using standard techniques. The purified factor consists of the TATA-binding protein and four TATA-binding protein-associated factors with relative molecular weights of 145,000, 99,000, 96,000, and 91,000. This yields a calculated native molecular weight of 460, 000, which compares well with its mass determined by scanning transmission electron microscopy (493,000) and its sedimentation rate, which is close to RNA polymerase I (515,000). Both impure and nearly homogeneous TIF-IB exhibit an apparent equilibrium dissociation constant of 56 +/- 3 pM. However, although impure TIF-IB can form a promoter-DNA complex resistant to challenge by other promoter-containing DNAs, near homogeneous TIF-IB cannot do so. An additional transcription factor, dubbed TIF-IE, restores the ability of near homogeneous TIF-IB to sequester DNA into a committed complex.
Radebaugh
C A
CA
Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, Colorado 80523-1870, USA.
Kubaska
W M
WM
Hoffman
L H
LH
Stiffler
K
K
Paule
M R
MR
D000048:Acanthamoeba / Q000235:genetics*; D000818:Animals; D002501:Centrifugation, Zonal; D002846:Chromatography, Affinity; D016054:DNA, Protozoan / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*; D035463:Pol1 Transcription Initiation Complex Proteins; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D012318:RNA Polymerase I / Q000378:metabolism; D035181:TATA-Box Binding Protein; D014157:Transcription Factors / Q000302:isolation & purification / Q000378:metabolism*; D014158:Transcription, Genetic
D016054:DNA, Protozoan; D004268:DNA-Binding Proteins; D035463:Pol1 Transcription Initiation Complex Proteins; D035181:TATA-Box Binding Protein; D014157:Transcription Factors; C063660:transcription initiation factor TIF-IB; D012318:RNA Polymerase I