Disease relevance of BRF1

• Mammalian TFIIIB can be separated into two fractions required for transcription of the adenovirus type 2 VAI gene, which have been designated 0.38M-TFIIIB and 0.48M-TFIIIB [1].

High impact information on BRF1

• CK2 associates with and normally activates the TATA binding protein (TBP) subunit of TFIIIB [2].
• Here we report that RNA polymerase (pol) III transcription is repressed in response to DNA damage by downregulation of TFIIIB, the core component of the pol III transcriptional machinery [2].
• A dominant mutation in the PCF4 gene of S. cerevisiae was isolated as a suppressor of a tRNA gene A block promoter mutation [3].
• The TFIIIB-dependent binding of pol III to the SUP4 tRNA and 5S rRNA genes has been analyzed in binary (protein and DNA only) and precisely arrested ternary (protein, DNA, and RNA) transcription complexes [4].
• Thus, TFIIIB is the sole transcription initiation factor of S. cerevisiae pol III; TFIIIC and TFIIIA are assembly factors for TFIIIB [4].

Biological context of BRF1

• Deletion of sequences at either the amino or carboxyl terminus of BRF1 gave both temperature- and cold-sensitive phenotypes [5].
• Our results suggest that the binding sites for BRF1 and TFIIIB90 on TBP-DNA both overlap the binding sites for TFIIA and TFIIB [6].
• Analysis of a 17.9 kb region from Saccharomyces cerevisiae chromosome VII reveals the presence of eight open reading frames, including BRF1 (TFIIIB70) and GCN5 genes [7].
• The Saccharomyces cerevisiae RNA polymerase III recruitment factor subunits Brf1 and Bdp1 impose a strict sequence preference for the downstream half of the TATA box [8].
• Using quantitative reverse transcription-polymerase chain reaction, 14-3-3 beta and BRF1 were found to be coexpressed in four different human tissues, suggesting a biologic role for their interaction in the regulation of cRaf-1-mediated signal transduction processes [9].

Associations of BRF1 with chemical compounds

• The heparin-resistant TFIIIB-DNA complex retains all three of its constituent proteins, TBP, BRF, and B" [10].
• The S. cerevisiae RNA polymerase III (pol III) transcription factor TFIIIB binds to DNA upstream of the transcription start site of the SUP4 tRNA(Tyr) gene in a TFIIIC-dependent reaction and to the major 5S rRNA gene in a reaction requiring TFIIIC and TFIIIA [4].
• These polypeptides were renatured after elution from sodium dodecyl sulfate-gels and tested individually and in combination for TFIIIB TAF activity [11].
• Selective inactivation of two components of the multiprotein transcription factor TFIIIB in cycloheximide growth-arrested yeast cells [12].
• Additionally Brf1 was identified as a target of repression in extracts of CPZ-treated cells [13].

Physical interactions of BRF1

• Finally, we demonstrate that BRF but not TFIIB binds the Pol III subunit C34 and we define a region of C34 necessary for this interaction [14].
• Transcription factor (TF) IIIB, the central transcription initiation factor of RNA polymerase III (pol III), is composed of three subunits, Bdp1, Brf1 and TATA-binding protein (TBP), all essential for normal function in vivo and in vitro [15].
• Dominant mutations in the ligand binding channel of the first TPR array, TPRs1-5, and on the back side of this array, increase Brf1 binding by Tfc4 [16].
• A promoter-deficient U6 RNA gene harboring GAL4-binding sites could be reactivated by fusing the GAL4 DNA-binding domain to components of the general transcription factor TFIIIC (tau) or TFIIIB [17].
• GCN4 effectively blocks initiation of transcription only when prebound to sites that overlap with the binding site of TFIIIB [18].

Regulatory relationships of BRF1

• Furthermore, TBP mutations that selectively inhibit Pol III transcription in vivo impair interactions between TBP and the BRF carboxy-terminal domain [14].

Other interactions of BRF1

• By assaying for interactions between BRF and other Pol III transcription factors, we show that it is able to bind to the 135-kD subunit of TFIIIC and also to TBP [14].
• Essential roles of Bdp1, a subunit of RNA polymerase III initiation factor TFIIIB, in transcription and tRNA processing [19].
• The interaction of yeast TFIIIB with the region upstream of the SUP4 tRNATyr gene was extensively probed by use of photoreactive phosphodiesters, deoxyuridines, and deoxycytidines that are site specifically incorporated into DNA [20].
• The sequence includes the BRF1 gene, encoding TFIIIB70, the 5' portion of the GCN5 gene, an open reading frame (ORF) previously identified as ORF MGA1, whose translation product shows similarity to heat-shock transcription factors and five new ORFs [7].
• Tfc4 contains two arrays of tetratricopeptide repeats (TPRs), each of which provides a binding site for Brf1 [16].

Analytical, diagnostic and therapeutic context of BRF1

• The individual TFIIIB subunits are nuclear by immunofluorescence and are calculated to have nuclear concentrations in the low micromolar range [21].
• This orientation of yeast TBP in Pol III promoter-bound TFIIIB is the same as in Pol II promoter-bound TFIID and in TBP-DNA complexes that have been analyzed by X-ray crystallography [22].
• To define the Pol III transcriptome in Saccharomyces cerevisiae, we performed genome-wide chromatin immunoprecipitation using subunits of Pol III, TFIIIB and TFIIIC [23].
• These findings together with the results from site-directed mutagenesis support the hypothesis that gain-of-function mutations at amino acid 190 in TPR2 stabilize an alternative conformation of TFIIIC131 that promotes its interaction with Brf1 [24].
• Additionally, biochemical fractionation of wild-type and mutant cell extracts shows that PCF1-1 increases the amount of the 70-kDa TFIIIB subunit detectable by Western (immunoblot) analysis in purified TFIIIB fractions and the transcription activity of a TFIIIB" fraction containing the 90-kDa subunit of this factor [25].

References