Identification of a domain within human TAF(I)48, a subunit of Selectivity Factor 1, that interacts with helix 2 of TBP

Taf1 N-terminal domain 2 (TAND2) of TFIID promotes formation of stable and mobile unstable TBP-TATA complexes

In eukaryotes, TATA-binding protein (TBP) occupancy of the core promoter globally correlates with transcriptional activity of class II genes. Elucidating how TBP is delivered to the TATA box or TATA-like element is crucial to understand the mechanisms of transcriptional regulation. A previous study demonstrated that the inhibitory DNA binding (IDB) surface of human TBP plays an indispensable role during the two-step formation of the TBP-TATA complex, first assuming an unstable and unbent intermediate conformation, and subsequently converting slowly to a stable and bent conformation. The DNA binding property of TBP is altered by physical contact of this surface with TBP regulators. In the present study, we examined whether the interaction between Taf1 N-terminal domain 2 (TAND2) and the IDB surface affected DNA binding property of yeast TBP by exploiting TAND2-fused TBP derivatives. TAND2 promoted formation of two distinct types of TBP-TATA complexes, which we arbitrarily designated as complex I and II. While complex I was stable and similar to the well-characterized original TBP-TATA complex, complex II was unstable and moved along DNA. Removal of TAND2 from TBP after complex formation revealed that continuous contact of TAND2 with the IDB surface was required for formation of complex II but not complex I. Further, TFIIA could be incorporated into the complex of TAND2-fused TBP and the TATA box, which was dependent on the amino-terminal non-conserved region of TBP, implying that this region could facilitate the exchange between TAND2 and TFIIA on the IDB surface. Collectively, these findings provide novel insights into the mechanism by which TBP is relieved from the interaction with TAND to bind the TATA box or TATA-like element within promoter-bound TFIID.

The transcriptional repressor activator protein Rap1p is a direct regulator of TATA-binding protein

Essentially all nuclear eukaryotic gene transcription depends upon the function of the transcription factor TATA-binding protein (TBP). Here we show that the abundant, multifunctional DNA binding transcription factor repressor activator protein Rap1p interacts directly with TBP. TBP-Rap1p binding occurs efficiently in vivo at physiological expression levels, and in vitro analyses confirm that this is a direct interaction. The DNA binding domains of the two proteins mediate interaction between TBP and Rap1p. TBP-Rap1p complex formation inhibits TBP binding to TATA promoter DNA. Alterations in either Rap1p or TBP levels modulate mRNA gene transcription in vivo. We propose that Rap1p represents a heretofore unrecognized regulator of TBP.

Reconfiguring the connectivity of a multiprotein complex: fusions of yeast TATA-binding protein with Brf1, and the function of transcription factor IIIB

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. Brf1 is a modular protein: Its N-proximal half is related to TFIIB and binds similarly to the C-terminal stirrup of TBP; its C-proximal one-third provides most of the affinity for TBP by binding along the entire length of the convex surface and N-terminal lateral face of TBP. A structure-informed triple fusion protein, with TBP core placed between the N- and C-proximal domains of Brf1, has been constructed. The Brf1-TBP triple fusion protein effectively replaces both Brf1 and TBP in TFIIIC-dependent and -independent transcription in vitro, and forms extremely stable TFIIIB-DNA complexes that are indistinguishable from wild-type TFIIIB-DNA complexes by chemical nuclease footprinting. Unlike Brf1 and TBP, the triple fusion protein is able to recruit pol III for TATA box-directed transcription of linear and supercoiled DNA in the absence of Bdp1. The Brf1-TBP triple fusion protein also effectively replaces Brf1 function in vivo as the intact protein, creating a TBP paralogue in yeast that is privatized for pol III transcription.

Mutational analysis of BTAF1-TBP interaction: BTAF1 can rescue DNA-binding defective TBP mutants

The BTAF1 transcription factor interacts with TATA-binding protein (TBP) to form the B–TFIID complex, which is involved in RNA polymerase II transcription. Here, we present an extensive mapping study of TBP residues involved in BTAF1 interaction. This shows that residues in the concave, DNA-binding surface of TBP are important for BTAF1 binding. In addition, BTAF1 interacts with residues in helix 2 on the convex side of TBP as assayed in protein–protein and in DNA-binding assays. BTAF1 drastically changes the TATA-box binding specificity of TBP, as it is able to recruit DNA-binding defective TBP mutants to both TATA-containing and TATA-less DNA. Interestingly, other helix 2 interacting factors, such as TFIIA and NC2, can also stabilize mutant TBP binding to DNA. In contrast, TFIIB which interacts with a distinct surface of TBP does not display this activity. Since many proteins contact helix 2 of TBP, this provides a molecular basis for mutually exclusive TBP interactions and stresses the importance of this structural element for eukaryotic transcription.