Separation of the transcriptional coactivator and antirepression functions of transcription factor IIA.

Abstract

Human transcription factor IIA (TFIIA) is composed of three subunits (a, f3, and y). TFIIA interacts with the TATA-box binding protein and can overcome repression of transcription. TFIIA was found to be necessary for VP16-mediated transcriptional activation through a coactivator function. We have separated the coactivator and antirepression activities of TFIIA. A TFIIA lacking the a subunit was isolated from HeLa cells. This "mini-TFIIA" interacts with the TATA-box binding protein and can overcome repression of transcription, but it is defective in transcriptional coactivator function.Initiation of transcription at promoters transcribed by RNA polymerase II (RNAPII) is complex. Different families of factors operate on these promoters (for a review, see ref. 1). One family of factors recognizes common promoter elements such as the TATA or the initiator motifs. These proteins are known as the basal, or general, transcription factors (GTFs) and include transcription factor IID (TFIID), TFIIB, TFIIE, TFIIF, and TFIIH (2). TFIID is the only GTF known to exhibit sequence-specific DNA binding activity, with specificity for the TATA element (3, 4). In vivo, TFIID exists as a large, multisubunit complex (5, 6), yet its DNA binding activity is intrinsic to only one polypeptide of 38 kDa, namely the TATA-box binding protein, TBP (7-9). The other subunits of TFIID are known as the TBP-associated factors, TAFs (10-12).A second class of factors that operate at promoters transcribed by RNAPII is composed of regulatory factors (13,14). One class of regulatory factors recognizes specific sequences located upstream or downstream of the TATA motifs (13-16). These factors can activate or repress transcription of specific genes upon binding to their sites. The molecular mechanisms by which regulatory factors regulate the activity of specific genes are poorly understood. Ultimately, regulatory factors encroach upon the basal transcription machinery to elicit their effect. In fact, some regulators have been shown to directly interact with components of the basal transcription machinery (1).Another growing family of transcription factors is known as coactivators (2, 17). Coactivators do not directly bind to promoter sequences (18), and they appear to function as "molecular bridges" between the basal transcription machinery and the promoter-bound activator. The prototype coactivators are the collection of TAFs in the TFIID complex (17). However, not all coactivators are subunits of the TFIID complex. Some coactivators are general, whereas others are activator-and tissue-specific. One such example is the B-cellspecific coactivator . Another collection of coactivators acts more generally, and they are required for optimal activation of transcription regardless of the activator type (23, 24). These general coactivators (cofactors) include some of the TAFs (25) (51,52). Moreover, the TBP-TFIIA interaction is important for activation of transcription in vivo (52). However, whether the different functions ascribed to TFIIA in activati...

TFIIA Interacts with TFIID via Association with TATA-Binding Protein and TAF40

“…The loss of interaction is not due to global changes in the structure of the protein, since these Toa2 derivatives interact normally with the other subunit of TFIIA (both in vivo and in vitro), are expressed in cells at levels similar to that in wild-type Toa2, and are functional for TFIIA-TBP interactions in vitro. Although the 4HB of TFIIA is not involved in either TBP or DNA interactions in the crystal structures, a deletion derivative of human TFIIA lacking two of the helices in this domain is not responsive to activators in vitro (54). Taken together with our results, this suggests that the 4HB domain of TFIIA is a functionally important target that facilitates formation of an active transcription initiation complex.…”

Retinoid X Receptor:Vitamin D3 Receptor Heterodimers Promote Stable Preinitiation Complex Formation and Direct 1,25-Dihydroxyvitamin D3-Dependent Cell-Free Transcription

“…7), we found that RXR:VDR facilitated the assembly of TBP:TFIIA, TBP:TFIIA:TFIIB, and TBP:TFIIB by recruitment into higher-mobility complexes on a VDRE-linked promoter and that 1,25(OH) 2 D 3 enhanced the formation of these complexes, particularly in the presence of TFIIA. Enhanced activator responsiveness mediated through TFIIA, especially in more defined transcription assays involv- ing TFIID, has previously been demonstrated and may be involved in counteracting inhibitory components of TFIID (17,61,108). While we cannot rule out contributions of RXR:VDR to elongation of transcription, as has been described for other activators (107), our results suggest that direct stabilization of GTF complexes by RXR:VDR is one way in which the receptors mediate transcriptional enhancement.…”

Selective Gene Expression in Magnocellular Neurons in Rat Supraoptic Nucleus

“…Among these are general transcription factor IIA (Roeder, 1991;Cortes et al, 1992;Ma et al, 1996), transcription factor E2A (Murre et al, 1989;Melloul et al, 2002), Hu antigen D (Keene, 2001;Perrone-Bizzozero and Bolognani, 2002;Park-Lee et al, 2003), and Sox 17 (Kanai et al, 1996;Kanai-Azuma et al, 2002). It is interesting that these widely expressed, transcriptionally related gene products are preferentially expressed in the SON relative to the hypothalamus, with expression ratios ranging from 3.8 to 5.1 (Table 2), again likely correlating with the high rates of transcription that occur in the SON (Burbach et al, 2001).…”