Family of proteins that interact with TFIID and regulate promoter activity

A conserved function of corepressors is to nucleate assembly of the transcriptional preinitiation complex

The plant corepressor TPL is recruited to diverse chromatin contexts, yet its mechanism of repression remains unclear. Previously, we have leveraged the fact that TPL retains its function in a synthetic transcriptional circuit in the yeast model Saccharomyces cerevisiae to localize repressive function to two distinct domains. Here, we employed two unbiased whole genome approaches to map the physical and genetic interactions of TPL at a repressed locus. We identified SPT4, SPT5 and SPT6 as necessary for repression with the SPT4 subunit acting as a bridge connecting TPL to SPT5 and SPT6. We also discovered the association of multiple additional constituents of the transcriptional preinitiation complex at TPL-repressed promoters, specifically those involved in early transcription initiation events. These findings were validated in yeast and plants through multiple assays, including a novel method to analyze conditional loss of function of essential genes in plants. Our findings support a model where TPL nucleates preassembly of the transcription activation machinery to facilitate rapid onset of transcription once repression is relieved.

Downregulation of transcription 1 hinders the replication of Dabie bandavirus by promoting the expression of TLR7, TLR8, and TLR9 signaling pathway

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a bunyavirus that causes SFTS, with a case fatality rate of up to 30 %. The innate immune system plays a crucial role in the defense against SFTSV; however, the impact of viral propagation of STFSV on the innate immune system remains unclear. Although proteomics analysis revealed that the expression of the downregulator of transcription 1 (DR1) increased after SFTSV infection, the specific change trend and the functional role of DR1 during viral infection remain unelucidated. In this study, we demonstrate that DR1 was highly expressed in response to SFTSV infection in HEK 293T cells using qRT-PCR and Western blot analysis. Furthermore, viral replication significantly increased the expression of various TLRs, especially TLR9. Our data indicated that DR1 positively regulated the expression of TLRs in HEK 293T cells, DR1 overexpression highly increased the expression of numerous TLRs, whereas RNAi-mediated DR1 silencing decreased TLR expression. Additionally, the myeloid differentiation primary response gene 88 (MyD88)-dependent or TIR-domain-containing adaptor inducing interferon-β (TRIF)-dependent signaling pathways were highly up- and downregulated by the overexpression and silencing of DR1, respectively. Finally, we report that DR1 stimulates the expression of TLR7, TLR8, and TLR9, thereby upregulating the TRIF-dependent and MyD88-dependent signaling pathways during the SFTSV infection, attenuating viral replication, and enhancing the production of type I interferon and various inflammatory factors, including IL-1β, IL-6, and IL-8. These results imply that DR1 defends against SFTSV replication by inducing the expression of TLR7, TLR8, and TLR9. Collectively, our findings revealed a novel role and mechanism of DR1 in mediating antiviral responses and innate immunity.

Ino2, activator of yeast phospholipid biosynthetic genes, interacts with basal transcription factors TFIIA and Bdf1

Binding of general transcription factors TFIID and TFIIA to basal promoters is rate-limiting for transcriptional initiation of eukaryotic protein-coding genes. Consequently, activator proteins interacting with subunits of TFIID and/or TFIIA can drastically increase the rate of initiation events. Yeast transcriptional activator Ino2 interacts with several Taf subunits of TFIID, among them the multifunctional Taf1 protein. In contrast to mammalian Taf1, yeast Taf1 lacks bromodomains which are instead encoded by separate proteins Bdf1 and Bdf2. In this work, we show that Bdf1 not only binds to acetylated histone H4 but can also be recruited by Ino2 and unrelated activators such as Gal4, Rap1, Leu3 and Flo8. An activator-binding domain was mapped in the N-terminus of Bdf1. Subunits Toa1 and Toa2 of yeast TFIIA directly contact sequences of basal promoters and TFIID subunit TBP but may also mediate the influence of activators. Indeed, Ino2 efficiently binds to two separate structural domains of Toa1, specifically with its N-terminal four-helix bundle structure required for dimerization with Toa2 and its C-terminal β-barrel domain contacting TBP and sequences of the TATA element. These findings complete the functional analysis of yeast general transcription factors Bdf1 and Toa1 and identify them as targets of activator proteins.

On the Role of TATA Boxes and TATA-Binding Protein in Arabidopsis thaliana

For transcription initiation by RNA polymerase II (Pol II), all eukaryotes require assembly of basal transcription machinery on the core promoter, a region located approximately in the locus spanning a transcription start site (-50; +50 bp). Although Pol II is a complex multi-subunit enzyme conserved among all eukaryotes, it cannot initiate transcription without the participation of many other proteins. Transcription initiation on TATA-containing promoters requires the assembly of the preinitiation complex; this process is triggered by an interaction of TATA-binding protein (TBP, a component of the general transcription factor TFIID (transcription factor II D)) with a TATA box. The interaction of TBP with various TATA boxes in plants, in particular Arabidopsis thaliana, has hardly been investigated, except for a few early studies that addressed the role of a TATA box and substitutions in it in plant transcription systems. This is despite the fact that the interaction of TBP with TATA boxes and their variants can be used to regulate transcription. In this review, we examine the roles of some general transcription factors in the assembly of the basal transcription complex, as well as functions of TATA boxes of the model plant A. thaliana. We review examples showing not only the involvement of TATA boxes in the initiation of transcription machinery assembly but also their indirect participation in plant adaptation to environmental conditions in responses to light and other phenomena. Examples of an influence of the expression levels of A. thaliana TBP1 and TBP2 on morphological traits of the plants are also examined. We summarize available functional data on these two early players that trigger the assembly of transcription machinery. This information will deepen the understanding of the mechanisms underlying transcription by Pol II in plants and will help to utilize the functions of the interaction of TBP with TATA boxes in practice.

Role of the TATA-box binding protein (TBP) and associated family members in transcription regulation

The assembly of transcription complexes on eukaryotic promoters involves a series of steps, including chromatin remodeling, recruitment of TATA-binding protein (TBP)-containing complexes, the RNA polymerase II holoenzyme, and additional basal transcription factors. This review describes the transcriptional regulation by TBP and its corresponding homologs that constitute the TBP family and their interactions with promoter DNA. The C-terminal core domain of TBP is highly conserved and contains two structural repeats that fold into a saddle-like structure, essential for the interaction with the TATA-box on DNA. Based on the TBP C-terminal core domain similarity, three TBP-related factors (TRFs) or TBP-like factors (TBPLs) have been discovered in metazoans, TRF1, TBPL1, and TBPL2. TBP is autoregulated, and once bound to DNA, repressors such as Mot1 induce TBP to dissociate, while other factors such as NC2 and the NOT complex convert the active TBP/DNA complex into inactive, negatively regulating TBP. TFIIA antagonizes the TBP repressors but may be effective only in conjunction with the RNA polymerase II holoenzyme recruitment to the promoter by promoter-bound activators. TRF1 has been discovered inDrosophila melanogasterandAnophelesbut found absent in vertebrates and yeast. TBPL1 cannot bind to the TATA-box; instead, TBPL1 prefers binding to TATA-less promoters. However, TBPL1 shows a stronger association with TFIIA than TBP. The TCT core promoter element is present in most ribosomal protein genes inDrosophilaand humans, and TBPL1 is required for the transcription of these genes. TBP directly participates in the DNA repair mechanism, and TBPL1 mediates cell cycle arrest and apoptosis. TBPL2 is closely related to its TBP paralog, showing 95% sequence similarity with the TBP core domain. Like TBP, TBPL2 also binds to the TATA-box and shows interactions with TFIIA, TFIIB, and other basal transcription factors. Despite these advances, much remains to be explored in this family of transcription factors.

TaDrAp1 and TaDrAp2, Partner Genes of a Transcription Repressor, Coordinate Plant Development and Drought Tolerance in Spelt and Bread Wheat

Down-regulator associated protein, DrAp1, acts as a negative cofactor (NC2α) in a transcription repressor complex together with another subunit, down-regulator Dr1 (NC2β). In binding to promotors and regulating the initiation of transcription of various genes, DrAp1 plays a key role in plant transition to flowering and ultimately in seed production. TaDrAp1 and TaDrAp2 genes were identified, and their expression and genetic polymorphism were studied using bioinformatics, qPCR analyses, a 40K Single nucleotide polymorphism (SNP) microarray, and Amplifluor-like SNP genotyping in cultivars of bread wheat (Triticum aestivum L.) and breeding lines developed from a cross between spelt (T. spelta L.) and bread wheat. TaDrAp1 was highly expressed under non-stressed conditions, and at flowering, TaDrAp1 expression was negatively correlated with yield capacity. TaDrAp2 showed a consistently low level of mRNA production. Drought caused changes in the expression of both TaDrAp1 and TaDrAp2 genes in opposite directions, effectively increasing expression in lower yielding cultivars. The microarray 40K SNP assay and Amplifluor-like SNP marker, revealed clear scores and allele discriminations for TaDrAp1 and TaDrAp2 and TaRht-B1 genes. Alleles of two particular homeologs, TaDrAp1-B4 and TaDrAp2-B1, co-segregated with grain yield in nine selected breeding lines. This indicated an important regulatory role for both TaDrAp1 and TaDrAp2 genes in plant growth, ontogenesis, and drought tolerance in bread and spelt wheat.

NC2 complex is a key factor for the activation of catalase-3 transcription by regulating H2A.Z deposition

Negative cofactor 2 (NC2), including two subunits NC2α and NC2β, is a conserved positive/negative regulator of class II gene transcription in eukaryotes. It is known that NC2 functions by regulating the assembly of the transcription preinitiation complex. However, the exact role of NC2 in transcriptional regulation is still unclear. Here, we reveal that, in Neurospora crassa, NC2 activates catalase-3 (cat-3) gene transcription in the form of heterodimer mediated by histone fold (HF) domains of two subunits. Deletion of HF domain in either of two subunits disrupts the NC2α–NC2β interaction and the binding of intact NC2 heterodimer to cat-3 locus. Loss of NC2 dramatically increases histone variant H2A.Z deposition at cat-3 locus. Further studies show that NC2 recruits chromatin remodeling complex INO80C to remove H2A.Z from the nucleosomes around cat-3 locus, resulting in transcriptional activation of cat-3. Besides HF domains of two subunits, interestingly, C-terminal repression domain of NC2β is required not only for NC2 binding to cat-3 locus, but also for the recruitment of INO80C to cat-3 locus and removal of H2A.Z from the nucleosomes. Collectively, our findings reveal a novel mechanism of NC2 in transcription activation through recruiting INO80C to remove H2A.Z from special H2A.Z-containing nucleosomes.

Architecture of the multi-functional SAGA complex and the molecular mechanism of holding TBP

In eukaryotes, transcription of protein encoding genes is initiated by the controlled deposition of the TATA-box binding protein TBP onto gene promoters, followed by the ordered assembly of a pre-initiation complex. The SAGA co-activator is a 19-subunit complex that stimulates transcription by the action of two chromatin-modifying enzymatic modules, a transcription activator binding module, and by delivering TBP. Recent cryo electron microscopy structures of yeast SAGA with bound nucleosome or TBP reveal the architecture of the different functional domains of the co-activator. An octamer of histone fold domains is found at the core of SAGA. This octamer, which deviates considerably from the symmetrical analogue forming the nucleosome, establishes a peripheral site for TBP binding where steric hindrance represses interaction with spurious DNA. The structures point to a mechanism for TBP delivery and release from SAGA that requires TFIIA and whose efficiency correlates with the affinity of DNA to TBP. These results provide a structural basis for understanding specific TBP delivery onto gene promoters and the role played by SAGA in regulating gene expression. The properties of the TBP delivery machine harboured by SAGA are compared with the TBP loading device present in the TFIID complex and show multiple similitudes.

SAGA and TFIID: Friends of TBP drifting apart

Transcription initiation constitutes a major checkpoint in gene regulation across all living organisms. Control of chromatin function is tightly linked to this checkpoint, which is best illustrated by the SAGA coactivator. This evolutionary conserved complex of 18-20 subunits was first discovered as a Gcn5p-containing histone acetyltransferase, but it also integrates a histone H2B deubiquitinase. The SAGA subunits are organized in a modular fashion around its central core. Strikingly, this central module of SAGA shares a number of proteins with the central core of the basal transcription factor TFIID. In this review I will compare the SAGA and TFIID complexes with respect to their shared subunits, structural organization, enzymatic activities and chromatin binding. I will place a special emphasis on the ancestry of SAGA and TFIID subunits, which suggests that these complexes evolved to control the activity of TBP (TATA-binding protein) in directing the assembly of transcription initiation complexes.

Aspergillus fumigatus Transcription Factors Involved in the Caspofungin Paradoxical Effect

Aspergillus fumigatus, one of the most important human-pathogenic fungal species, is able to cause aspergillosis, a heterogeneous group of diseases that presents a wide range of clinical manifestations. Invasive pulmonary aspergillosis is the most serious pathology in terms of patient outcome and treatment, with a high mortality rate ranging from 50% to 95% primarily affecting immunocompromised patients. Azoles have been used for many years as the main antifungal agents to treat and prevent invasive aspergillosis. However, there were several reports of evolution of clinical azole resistance in the last decade. Caspofungin, a noncompetitive β-1,3-glucan synthase inhibitor, has been used against A. fumigatus, but it is fungistatic and is recommended as second-line therapy for invasive aspergillosis. More information about caspofungin tolerance and resistance is necessary in order to refine antifungal strategies that target the fungal cell wall. Here, we screened a transcription factor (TF) deletion library for TFs that can mediate caspofungin tolerance and resistance. We have identified 11 TFs that are important for caspofungin sensitivity and/or for the caspofungin paradoxical effect (CPE). These TFs encode proteins involved in the basal modulation of the RNA polymerase II initiation sites, calcium metabolism or cell wall remodeling, and mitochondrial respiratory function. The study of those genes regulated by TFs identified in this work will provide a better understanding of the signaling pathways that are important for caspofungin tolerance and resistance.

Aspergillus fumigatus is the leading cause of pulmonary fungal diseases. Azoles have been used for many years as the main antifungal agents to treat and prevent invasive aspergillosis. However, in the last 10 years there have been several reports of azole resistance in A. fumigatus and new strategies are needed to combat invasive aspergillosis. Caspofungin is effective against other human-pathogenic fungal species, but it is fungistatic only against A. fumigatus. Resistance to caspofungin in A. fumigatus has been linked to mutations in the fksA gene that encodes the target enzyme of the drug β-1,3-glucan synthase. However, tolerance of high caspofungin concentrations, a phenomenon known as the caspofungin paradoxical effect (CPE), is also important for subsequent adaptation and drug resistance evolution. Here, we identified and characterized the transcription factors involved in the response to CPE by screening an A. fumigatus library of 484 null transcription factors (TFs) in CPE drug concentrations. We identified 11 TFs that had reduced CPE and that encoded proteins involved in the basal modulation of the RNA polymerase II initiation sites, calcium metabolism, and cell wall remodeling. One of these TFs, FhdA, was important for mitochondrial respiratory function and iron metabolism. The ΔfhdA mutant showed decreased growth when exposed to Congo red or to high temperature. Transcriptome sequencing (RNA-seq) analysis and further experimental validation indicated that the ΔfhdA mutant showed diminished respiratory capacity, probably affecting several pathways related to the caspofungin tolerance and resistance. Our results provide the foundation to understand signaling pathways that are important for caspofungin tolerance and resistance.

The negative cofactor 2 complex is a key regulator of drug resistance in Aspergillus fumigatus

The frequency of antifungal resistance, particularly to the azole class of ergosterol biosynthetic inhibitors, is a growing global health problem. Survival rates for those infected with resistant isolates are exceptionally low. Beyond modification of the drug target, our understanding of the molecular basis of azole resistance in the fungal pathogen Aspergillus fumigatus is limited. We reasoned that clinically relevant antifungal resistance could derive from transcriptional rewiring, promoting drug resistance without concomitant reductions in pathogenicity. Here we report a genome-wide annotation of transcriptional regulators in A. fumigatus and construction of a library of 484 transcription factor null mutants. We identify 12 regulators that have a demonstrable role in itraconazole susceptibility and show that loss of the negative cofactor 2 complex leads to resistance, not only to the azoles but also the salvage therapeutics amphotericin B and terbinafine without significantly affecting pathogenicity.

Resistance to primary treatments of invasive aspergillosis is growing. Here, the authors generate a knockout library for 484 transcription factors in Aspergillus fumigatus, and show that loss of the NCT complex leads to cross-resistance to all primary and some salvage therapeutics without affecting pathogenicity.

Promoter Recognition: Putting TFIID on the Spot

Basal transcription factor TFIID connects transcription activation to the assembly of the RNA polymerase II preinitiation complex at the core promoter of genes. The mechanistic understanding of TFIID function and dynamics has been limited by the lack of high-resolution structures of the holo-TFIID complex. Recent cryo-electron microscopy studies of yeast and human TFIID complexes provide insight into the molecular organization and structural dynamics of this highly conserved transcription factor. Here, we discuss how these TFIID structures provide new paradigms for: (i) the dynamic recruitment of TFIID; (ii) the binding of TATA-binding protein (TBP) to promoter DNA; (iii) the multivalency of TFIID interactions with (co)activators, nucleosomes, or promoter DNA; and (iv) the opportunities for regulation of TBP turnover and promoter dynamics.

Analyzing the Dynamics of Single TBP-DNA-NC2 Complexes Using Hidden Markov Models

Single-pair Förster resonance energy transfer (spFRET) has become an important tool for investigating conformational dynamics in biological systems. To extract dynamic information from the spFRET traces measured with total internal reflection fluorescence microscopy, we extended the hidden Markov model (HMM) approach. In our extended HMM analysis, we incorporated the photon-shot noise from camera-based systems into the HMM. Thus, the variance in Förster resonance energy transfer (FRET) efficiency of the various states, which is typically a fitted parameter, is explicitly included in the analysis estimated from the number of detected photons. It is also possible to include an additional broadening of the FRET state, which would then only reflect the inherent flexibility of the dynamic biological systems. This approach is useful when comparing the dynamics of individual molecules for which the total intensities vary significantly. We used spFRET with the extended HMM analysis to investigate the dynamics of TATA-box-binding protein (TBP) on promoter DNA in the presence of negative cofactor 2 (NC2). We compared the dynamics of two promoters as well as DNAs of different length and labeling location. For the adenovirus major late promoter, four FRET states were observed; three states correspond to different conformations of the DNA in the TBP-DNA-NC2 complex and a four-state model in which the complex has shifted along the DNA. The HMM analysis revealed that the states are connected via a linear, four-well model. For the H2B promoter, more complex dynamics were observed. By clustering the FRET states detected with the HMM analysis, we could compare the general dynamics observed for the two promoter sequences. We observed that the dynamics from a stretched DNA conformation to a bent conformation for the two promoters were similar, whereas the bent conformation of the TBP-DNA-NC2 complex for the H2B promoter is approximately three times more stable than for the adenovirus major late promoter.

The global regulator Ncb2 escapes from the core promoter and impacts transcription in response to drug stress in Candida albicans

Ncb2, the β subunit of NC2 complex, a heterodimeric regulator of transcription was earlier shown to be involved in the activated transcription of CDR1 gene in azole resistant isolate (AR) of Candida albicans. This study examines its genome-wide role by profiling Ncb2 occupancy between genetically matched pair of azole sensitive (AS) and AR clinical isolates. A comparison of Ncb2 recruitment between the two isolates displayed that 29 genes had higher promoter occupancy of Ncb2 in the AR isolate. Additionally, a host of genes exhibited exclusive occupancy of Ncb2 at promoters of either AR or AS isolate. The analysis also divulged new actors of multi-drug resistance, whose transcription was activated owing to the differential occupancy of Ncb2. The conditional, sequence-specific positional escape of Ncb2 from the core promoter in AS isolate and its preferential recruitment to the core promoter of certain genes in AR isolates was most noteworthy means of transcription regulation. Together, we show that positional rearrangement of Ncb2 resulting in either activation or repression of gene expression in response to drug-induced stress, represents a novel regulatory mechanism that opens new opportunities for therapeutic intervention to prevent development of drug tolerance in C. albicans cells.

Reversal of platinum drug resistance by the histone deacetylase inhibitor belinostat

OBJECTIVES

To investigate and elucidate the mechanism for the potentiation of cisplatin anticancer activity by belinostat in platinum (Pt)-resistant lung cancer cells.

MATERIALS AND METHODS

Combination of cisplatin and belinostat was investigated in two pairs of parental and cisplatin-resistant non-small cell lung cancer (NSCLC) cell lines. The Pt-resistant cell models exhibited overexpression of the efflux transporter ABCC2 and enhanced DNA repair capacity. Cellular accumulation of cisplatin and extent of DNA platination were measured by inductively coupled plasma optical emission spectrometer. Expression of Pt transporters and DNA repair gene were determined by quantitative real-time PCR. Inhibition of ABCC2 transport activity was examined by flow cytometric assay. Regulation of ABCC2 at the promoter level was studied by chromatin immunoprecipitation assay.

RESULTS AND CONCLUSION

In Pt-resistant lung cancer cells, belinostat apparently circumvent the resistance through inhibition of both ABCC2 and DNA repair-mediated mechanisms. The combination of belinostat and cisplatin were found to display synergistic cytotoxic effect in cisplatin-resistant lung cancer cell lines when the two drugs were added concomitantly or when belinostat was given before cisplatin. Upon the concomitant administration of belinostat, cellular accumulation of cisplatin and formation of DNA-Pt adducts were found to be increased whereas expression levels of the efflux transporter ABCC2 and the DNA repair gene ERCC1 were inhibited in Pt-resistant cells. Belinostat-mediated downregulation of ABCC2 was associated with an increase association of a transcriptional repressor (negative cofactor 2) but reduced association of a transcriptional activator (TFIIB) to the ABCC2 promoter. The data advocates the use of belinostat as a novel drug resistance reversal agent for use in combination cancer chemotherapeutic regimens.

Fcγ1 fragment of IgG1 as a powerful affinity tag in recombinant Fc-fusion proteins: immunological, biochemical and therapeutic properties

Affinity tags are vital tools for the production of high-throughput recombinant proteins. Several affinity tags, such as the hexahistidine tag, maltose-binding protein, streptavidin-binding peptide tag, calmodulin-binding peptide, c-Myc tag, glutathione S-transferase and FLAG tag, have been introduced for recombinant protein production. The fragment crystallizable (Fc) domain of the IgG1 antibody is one of the useful affinity tags that can facilitate detection, purification and localization of proteins and can improve the immunogenicity, modulatory effects, physicochemical and pharmaceutical properties of proteins. Fcγ recombinant forms a group of recombinant proteins called Fc-fusion proteins (FFPs). FFPs are widely used in drug discovery, drug delivery, vaccine design and experimental research on receptor-ligand interactions. These fusion proteins have become successful alternatives to monoclonal antibodies for drug developments. In this review, the physicochemical, biochemical, immunological, pharmaceutical and therapeutic properties of recombinant FFPs were discussed as a new generation of bioengineering strategies.

Structural basis for recognition and remodeling of the TBP:DNA:NC2 complex by Mot1

Swi2/Snf2 ATPases remodel substrates such as nucleosomes and transcription complexes to control a wide range of DNA-associated processes, but detailed structural information on the ATP-dependent remodeling reactions is largely absent. The single subunit remodeler Mot1 (modifier of transcription 1) dissociates TATA box-binding protein (TBP):DNA complexes, offering a useful system to address the structural mechanisms of Swi2/Snf2 ATPases. Here, we report the crystal structure of the N-terminal domain of Mot1 in complex with TBP, DNA, and the transcription regulator negative cofactor 2 (NC2). Our data show that Mot1 reduces DNA:NC2 interactions and unbends DNA as compared to the TBP:DNA:NC2 state, suggesting that Mot1 primes TBP:NC2 displacement in an ATP-independent manner. Electron microscopy and cross-linking data suggest that the Swi2/Snf2 domain of Mot1 associates with the upstream DNA and the histone fold of NC2, thereby revealing parallels to some nucleosome remodelers. This study provides a structural framework for how a Swi2/Snf2 ATPase interacts with its substrate DNA:protein complex.

DOI:http://dx.doi.org/10.7554/eLife.07432.001

An organism’s DNA contains thousands of genes, not all of which are active at the same time. Cells use a number of methods to carefully control when particular genes are switched on or off. For example, proteins called transcription factors can activate a gene by binding to particular regions of DNA called promoters. One such transcription factor is called the TATA-binding protein (TBP for short). Mot1 is a remodeling enzyme that can form a “complex” with TBP by binding to it, and in doing so remove TBP from DNA. This silences the genes at those sites. The freed TBP can then bind to other promoters that lack Mot1 and activate the genes found there.

In 2011, researchers revealed the structure of the complex formed between TBP and Mot1 after TBP has been detached from DNA. However, the structure of the complex that forms while TBP is still bound to the DNA molecule was not known. Butryn et al. – including several of the researchers involved in the 2011 work – have now described the structure of this complex using X-ray crystallography and electron microscopy. Another protein called negative cofactor 2 is also part of the complex, and helps to stabilize it.

Butryn et al. found that Mot1 reduces the strength of the interactions between DNA and both TBP and negative cofactor 2. Binding to TBP and negative cofactor 2 causes the DNA molecule to bend; however, if Mot1 is also in the complex, the DNA becomes less bent. By making these changes, Mot1 is likely to prime TBP to detach from the DNA. Since the current structures do not yet reveal the atomic structure of Mot1’s ATP dependent DNA motor domain, the next challenge is to visualize the entire complex at atomic resolution.

DOI:http://dx.doi.org/10.7554/eLife.07432.002

Suppression of intragenic transcription requires the MOT1 and NC2 regulators of TATA-binding protein

Chromatin structure in transcribed regions poses a barrier for intragenic transcription. In a comprehensive study of the yeast chromatin remodelers and the Mot1p-NC2 regulators of TATA-binding protein (TBP), we detected synthetic genetic interactions indicative of suppression of intragenic transcription. Conditional depletion of Mot1p or NC2 in absence of the ISW1 remodeler, but not in the absence of other chromatin remodelers, activated the cryptic FLO8 promoter. Likewise, conditional depletion of Mot1p or NC2 in deletion backgrounds of the H3K36 methyltransferase Set2p or the Asf1p-Rtt106p histone H3-H4 chaperones, important factors involved in maintaining a repressive chromatin environment, resulted in increased intragenic FLO8 transcripts. Activity of the cryptic FLO8 promoter is associated with reduced H3 levels, increased TBP binding and tri-methylation of H3K4 and is independent of Spt-Ada-Gcn5-acetyltransferase function. These data reveal cooperation of negative regulation of TBP with specific chromatin regulators to inhibit intragenic transcription.

Transcriptional/epigenetic regulator CBP/p300 in tumorigenesis: structural and functional versatility in target recognition

In eukaryotic cells, gene transcription is regulated by sequence-specific DNA-binding transcription factors that recognize promoter and enhancer elements near the transcriptional start site. Some coactivators promote transcription by connecting transcription factors to the basal transcriptional machinery. The highly conserved coactivators CREB-binding protein (CBP) and its paralog, E1A-binding protein (p300), each have four separate transactivation domains (TADs) that interact with the TADs of a number of DNA-binding transcription activators as well as general transcription factors (GTFs), thus mediating recruitment of basal transcription machinery to the promoter. Most promoters comprise multiple activator-binding sites, and many activators contain tandem TADs, thus multivalent interactions may stabilize CBP/p300 at the promoter, and intrinsically disordered regions in CBP/p300 and many activators may confer adaptability to these multivalent complexes. CBP/p300 contains a catalytic histone acetyltransferase (HAT) domain, which remodels chromatin to 'relax' its superstructure and enables transcription of proximal genes. The HAT activity of CBP/p300 also acetylates some transcription factors (e.g., p53), hence modulating the function of key transcriptional regulators. Through these numerous interactions, CBP/p300 has been implicated in complex physiological and pathological processes, and, in response to different signals, can drive cells towards proliferation or apoptosis. Dysregulation of the transcriptional and epigenetic functions of CBP/p300 is associated with leukemia and other types of cancer, thus it has been recognized as a potential anti-cancer drug target. In this review, we focus on recent exciting findings in the structural mechanisms of CBP/p300 involving multivalent and dynamic interactions with binding partners, which may pave new avenues for anti-cancer drug development.

Core promoter-selective coregulators of transcription by RNA polymerase II

The core promoter of eukaryotic genes is structurally and functionally diverse and contributes to the combinatorial control of gene-specific transcription. Recent findings identifying specific coactivators and architectural proteins as core promoter-specific basal cofactors for RNA polymerase II suggest possible mechanisms for the core promoter selectivity of certain regulators and enhancers.

A BEN-domain-containing protein associates with heterochromatin and represses transcription

In eukaryotes, higher order chromatin structure governs crucial cellular processes including DNA replication, transcription and post-transcriptional gene regulation. Specific chromatin-interacting proteins play vital roles in the maintenance of chromatin structure. We have identified BEND3, a quadruple BEN domain-containing protein that is highly conserved amongst vertebrates. BEND3 colocalizes with HP1 and H3 trimethylated at K9 at heterochromatic regions in mammalian cells. Using an in vivo gene locus, we have been able to demonstrate that BEND3 associates with the locus only when it is heterochromatic and dissociates upon activation of transcription. Furthermore, tethering BEND3 inhibits transcription from the locus, indicating that BEND3 is involved in transcriptional repression through its interaction with histone deacetylases and Sall4, a transcription repressor. We further demonstrate that BEND3 is SUMOylated and that such modifications are essential for its role in transcriptional repression. Finally, overexpression of BEND3 causes premature chromatin condensation and extensive heterochromatinization, resulting in cell cycle arrest. Taken together, our data demonstrate the role of a novel heterochromatin-associated protein in transcriptional repression.

Genome-wide prediction and analysis of human chromatin boundary elements

Boundary elements partition eukaryotic chromatin into active and repressive domains, and can also block regulatory interactions between domains. Boundary elements act via diverse mechanisms making accurate feature-based computational predictions difficult. Therefore, we developed an unbiased algorithm that predicts the locations of human boundary elements based on the genomic distributions of chromatin and transcriptional states, as opposed to any intrinsic characteristics that they may possess. Application of our algorithm to ChIP-seq data for histone modifications and RNA Pol II-binding data in human CD4(+) T cells resulted in the prediction of 2542 putative chromatin boundary elements genome wide. Predicted boundary elements display two distinct features: first, position-specific open chromatin and histone acetylation that is coincident with the recruitment of sequence-specific DNA-binding factors such as CTCF, EVI1 and YYI, and second, a directional and gradual increase in histone lysine methylation across predicted boundaries coincident with a gain of expression of non-coding RNAs, including examples of boundaries encoded by tRNA and other non-coding RNA genes. Accordingly, a number of the predicted human boundaries may function via the synergistic action of sequence-specific recruitment of transcription factors leading to non-coding RNA transcriptional interference and the blocking of facultative heterochromatin propagation by transcription-associated chromatin remodeling complexes.

Ncb2 is involved in activated transcription of CDR1 in azole-resistant clinical isolates of Candida albicans

We recently demonstrated that CDR1 overexpression in azole-resistant isolates of Candida albicans is due to its enhanced transcriptional activation and increased mRNA stability. In this study, we provide the first evidence of transcriptional regulation of CDR1 by Ncb2, the β subunit of NC2, a heterodimeric regulator of transcription. Conditional NCB2 null mutants displayed decreased susceptibility toward azole and an enhanced transcription of CDR1. Interestingly, Ncb2 associated with the CDR1 promoter under both repression and activation; however, an increase in recruitment was observed under both transient and constitutive activation states. By chromatin immunoprecipitation (ChIP) assay, we showed the preferential recruitment of Ncb2 to the core TATA region under activation (azole-resistant isolate), while under repression (azole-susceptible isolate) it was present at the TATA upstream region. Further, ChIP analysis revealed that Ncb2 binding was not restricted to the CDR1 gene; instead, it was observed on the promoters of genes coregulated with CDR1 by the transcription activator Tac1. The tac1Δ null mutants, which fail to show the drug-induced transient activation of CDR1, also showed no increase in Ncb2 recruitment at the promoter. Taken together, our results show that Ncb2, in conjunction with Tac1, is involved in the transcriptional activation of CDR1, opening up new therapeutic possibilities to combat multidrug resistance (MDR) in C. albicans.

Mediator-dependent nuclear receptor function

As gene-specific transcription factors, nuclear receptors are broadly involved in many important biological processes. Their function on target genes requires the stepwise assembly of different coactivator complexes that facilitate chromatin remodeling and subsequent preinitiation complex (PIC) formation and function. Mediator has proved to be a crucial, and general, nuclear receptor-interacting coactivator, with demonstrated functions in transcription steps ranging from chromatin remodeling to subsequent PIC formation and function. Here we discuss our current understanding of (i) pathways involved in Mediator recruitment and function through nuclear receptor target gene enhancers and promoters, (ii) conditional requirements for the strong nuclear receptor-Mediator interactions mediated by NR AF2 domains and the MED1 LXXLL motifs, (iii) Mediator functions, through different nuclear receptor-interacting subunits, in different metabolic pathways, (iv) emerging functions of Mediator as a corepressor in addition to its major role as a coactivator and (v) mechanisms by which Mediator acts to transmit signals from enhancer-bound nuclear receptors to the general transcription machinery at core promoters to effect PIC formation and function. As a nuclear receptor coregulator with increasingly diverse functions, Mediator may thus modulate nuclear receptor signaling through several different mechanisms.

Marine natural product aurilide activates the OPA1-mediated apoptosis by binding to prohibitin

Aurilide is a potent cytotoxic marine natural product that induces apoptosis in cultured human cells at the picomolar to nanomolar range; however, its mechanism of action has been unknown. Results of the present study showed that aurilide selectively binds to prohibitin 1 (PHB1) in the mitochondria, activating the proteolytic processing of optic atrophy 1 (OPA1) and resulting in mitochondria-induced apoptosis. The mechanism of aurilide cytotoxicity suggests that PHB1 is an apoptosis-regulating protein amenable to modulation by small molecules. Aurilide may serve as a small-molecule tool for studies of mitochondria-induced apoptosis.

The metazoan ATAC and SAGA coactivator HAT complexes regulate different sets of inducible target genes

Histone acetyl transferases (HATs) play a crucial role in eukaryotes by regulating chromatin architecture and locus-specific transcription. The GCN5 HAT was identified as a subunit of the SAGA (Spt-Ada-Gcn5-Acetyltransferase) multiprotein complex. Vertebrate cells express a second HAT, PCAF, that is 73% identical to GCN5. Here, we report the characterization of the mammalian ATAC (Ada-Two-A-Containing) complexes containing either GCN5 or PCAF in a mutually exclusive manner. In vitro ATAC complexes acetylate lysine 14 of histone H3. Moreover, ATAC- or SAGA-specific knock-down experiments suggest that both ATAC and SAGA are involved in the acetylation of histone H3K9 and K14 residues. Despite their catalytic similarities, SAGA and ATAC execute their coactivator functions on distinct sets of inducible target genes. Interestingly, ATAC strongly influences the global phosphorylation level of histone H3S10, suggesting that in mammalian cells a cross-talk exists linking ATAC function to H3S10 phosphorylation.

Dr1 (NC2) is present at tRNA genes and represses their transcription in human cells

Dr1 (also known as NC2β) was identified as a repressor of RNA polymerase (pol) II transcription. It was subsequently shown to inhibit pol III transcription when expressed at high levels in vitro or in yeast cells. However, endogenous Dr1 was not detected at pol III-transcribed genes in growing yeast. In contrast, we demonstrate that endogenous Dr1 is present at pol III templates in human cells, as is its dimerization partner DRAP1 (also called NC2α). Expression of tRNA by pol III is selectively enhanced by RNAi-mediated depletion of endogenous human Dr1, but we found no evidence that DRAP1 influences pol III output in vivo. A stable association was detected between endogenous Dr1 and the pol III-specific transcription factor Brf1. This interaction may recruit Dr1 to pol III templates in vivo, as crosslinking to these sites increases following Brf1 induction. On the basis of these data, we conclude that the physiological functions of human Dr1 include regulation of pol III transcription.

Regulation of nuclear import and export of negative cofactor 2

The negative cofactor 2 (NC2) is a protein complex composed of two subunits, NC2alpha and NC2beta, and plays a key role in transcription regulation. Here we investigate whether each subunit contains a nuclear localization signal (NLS) that permits individual crossing of the nuclear membrane or whether nuclear import of NC2alpha and NC2beta depends on heterodimerization. Our results from in vitro binding studies and transfection experiments in cultured cells show that each subunit contains a classical NLS (cNLS) that is recognized by the importin alpha/beta heterodimer. Regardless of the individual cNLSs the two NC2 subunits are translocated as a preassembled complex as co-transfection experiments with wild-type and cNLS-deficient NC2 subunits demonstrate. Ran-dependent binding of the nuclear export receptor Crm1/exportin 1 confirmed the presence of a leucine-rich nuclear export signal (NES) in NC2beta. In contrast, NC2alpha does not exhibit a NES. Our results from interspecies heterokaryon assays suggest that heterodimerization with NC2alpha masks the NES in NC2beta, which prevents nuclear export of the NC2 complex. A mutation in either one of the two cNLSs decreases the extent of importin alpha/beta-mediated nuclear import of the NC2 complex. In addition, the NC2 complex can enter the nucleus via a second pathway, facilitated by importin 13. Because importin 13 binds exclusively to the NC2 complex but not to the individual subunits this alternative import pathway depends on sequence elements distributed among the two subunits.

The dynamic personality of TATA-binding protein

TATA-binding protein (TBP) is a central component of the transcription apparatus and its association with promoters is dynamically regulated genome-wide. Recent work has shed new light on the functional specificity of Mot1 and NC2, two factors that control TBP distribution and activity. These studies underscore how regulation of TBP globally influences fundamental aspects of gene expression, including the balance of transcriptional output from different types of promoters, and the amplitude and timing of gene activation.

Roles of coactivator proteins in dioxin induction of CYP1A1 and CYP1B1 in human breast cancer cells

Cytochrome P450 (CYP) 1A1 and CYP1B1 are inducible by 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin) in the human breast cancer cell line, MCF-7. Since CYP1A1 was inducible to a much greater degree than CYP1B1, we hypothesized that there may be differences in coactivator recruitment to the promoter and/or enhancer regions of these genes. Dioxin treatment leads to recruitment of the aryl hydrocarbon receptor to the enhancer regions but not to the proximal promoter regions of both the CYP1A1 and CYP1B1 genes. On the other hand, dioxin treatment facilitated recruitment of RNA polymerase II to the promoters but not the enhancer regions. Dioxin treatment also elicited recruitment of the transcriptional coactivators, steroid receptor coactivator 1 (SRC-1) and steroid receptor coactivator 2 (SRC-2) and p300, which possess intrinsic histone acetyltranferase activities, to both genes, whereas Brahma (BRM)/Switch 2-related gene 1 (BRG-1), a subunit of nucleosomal remodeling factors, was recruited more robustly to CYP1A1 relative to CYP1B1. Small inhibitory RNA-mediated knockdown of p300 and SRC-2 adversely affected dioxin induction of both genes, whereas knockdown of BRM/BRG-1 reduced CYP1A1 induction but had little, if any, effect on CYP1B1 induction. These results suggest that nucleosomal remodeling is less significant for dioxin-mediated induction of CYP1B1 than that of CYP1A1 and may be related to the more modest inducibility of the former. Interestingly, simultaneous knockdown of SRC-2 and BRM/BRG-1 had no greater effect on CYP1A1 induction than knockdown of each coactivator individually, while simultaneous knockdown of p300 and BRM/BRG-1 had a much greater effect than knockdown of each individual gene, suggesting that the recruitment of SRC-2 to CYP1A1 depends upon BRM/BRG-1, while the recruitments of p300 and BRM/BRG-1 are independent of each other. These observations provide novel insights into the functional roles of the endogenous coactivators in dioxin induction of the human CYP1A1 and CYP1B1 genes in their natural chromosomal configurations.

Human ATAC Is a GCN5/PCAF-containing acetylase complex with a novel NC2-like histone fold module that interacts with the TATA-binding protein

Eukaryotic GCN5 acetyltransferases influence diverse biological processes by acetylating histones and non-histone proteins and regulating chromatin and gene-specific transcription as part of multiprotein complexes. In lower eukaryotes and invertebrates, these complexes include the yeast ADA complex that is still incompletely understood; the SAGA (Spt-Ada-Gcn5 acetylase) complexes from yeast to Drosophila that are mostly coactivators; and the ATAC (Ada Two-A containing) complex, only known in Drosophila and still poorly characterized. In contrast, vertebrate organisms, express two paralogous GCN5-like acetyltransferases (GCN5 and PCAF), which have been found so far only in SAGA-type complexes referred to hereafter as the STAGA (SPT3-TAF9-GCN5/PCAF acetylase) complexes. We now report the purification and characterization of vertebrate (human) ATAC-type complexes and identify novel components of STAGA. We show that human ATAC complexes incorporate in addition to GCN5 or PCAF (GCN5/PCAF), other epigenetic coregulators (ADA2-A, ADA3, STAF36, and WDR5), cofactors of chromatin assembly/remodeling and DNA replication machineries (POLE3/CHRAC17 and POLE4), the stress- and TGFbeta-activated protein kinase (TAK1/MAP3K7) and MAP3-kinase regulator (MBIP), additional cofactors of unknown function, and a novel YEATS2-NC2beta histone fold module that interacts with the TATA-binding protein (TBP) and negatively regulates transcription when recruited to a promoter. We further identify the p38 kinase-interacting protein (p38IP/FAM48A) as a novel component of STAGA with distant similarity to yeast Spt20. These results suggest that vertebrate ATAC-type and STAGA-type complexes link specific extracellular signals to modification of chromatin structure and regulation of the basal transcription machinery.

Function and structural organization of Mot1 bound to a natural target promoter

Mot1 is an essential, conserved TATA-binding protein (TBP)-associated factor in Saccharomyces cerevisiae and a member of the Snf2/Swi2 ATPase family. Mot1 uses ATP hydrolysis to displace TBP from DNA, an activity that can be readily reconciled with its global role in gene repression. Less well understood is how Mot1 directly activates gene expression. It has been suggested that Mot1-mediated activation can occur by displacement of inactive TBP-containing complexes from promoters, thereby permitting assembly of functional transcription complexes. Mot1 may also activate transcription by other mechanisms that have not yet been defined. A gap in our understanding has been the absence of biochemical information related to the activity of Mot1 on natural target genes. Using URA1 as a model Mot1-activated promoter, we show striking differences in the way that both TBP and Mot1 interact with DNA compared with other model DNA substrates analyzed previously. These differences are due at least in part to the propensity of TBP alone to bind to the URA1 promoter in the wrong orientation to direct appropriate assembly of the URA1 preinitiation complex. The results suggest that Mot1-mediated activation of URA1 transcription involves at least two steps, one of which is the removal of TBP bound to the promoter in the opposite orientation required for URA1 transcription.

NC2 mobilizes TBP on core promoter TATA boxes

The general transcription factors (GTFs) of eukaryotic RNA polymerase II, in a process facilitated by regulatory and accessory factors, target promoters through synergistic interactions with core elements. The specific binding of the TATA box-binding protein (TBP) to the TATA box has led to the assumption that GTFs recognize promoters directly, producing a preinitiation complex at a defined position. Using biochemical analysis as well as biophysical single-pair Förster resonance energy transfer, we now provide evidence that negative cofactor-2 (NC2) induces dynamic conformational changes in the TBP-DNA complex that allow it to escape and return to TATA-binding mode. This can lead to movement of TBP along the DNA away from TATA.

The initiator core promoter element antagonizes repression of TATA-directed transcription by negative cofactor NC2

Core promoter regions of protein-coding genes in metazoan genomes are structurally highly diverse and can contain several distinct core promoter elements, which direct accurate transcription initiation and determine basal promoter strength. Diversity in core promoter structure is an important aspect of transcription regulation in metazoans as it provides a basis for gene-selective function of activators and repressors. The basal activity of TATA box-containing promoters is dramatically enhanced by the initiator element (INR), which can function in concert with the TATA box in a synergistic manner. Here we report that a functional INR provides resistance to NC2 (Dr1/DRAP1), a general repressor of TATA promoters. INR-mediated resistance to NC2 is established during transcription initiation complex assembly and requires TBP-associated factors (TAFs) and TAF- and INR-dependent cofactor activity. Remarkably, the INR appears to stimulate TATA-dependent transcription similar to activators by strongly enhancing recruitment of TFIIA and TFIIB and, at the same time, by compromising NC2 binding.

INTERACTION OF RECOMBINANT TATA-BINDING PROTEIN WITH MAMMALS GENES PROMOTER TATA

Quantitative characteristics of interaction recombinant TATA-binding protein (TBP) with oligonucleotides identical to natural TATA-containing promoter region genes of mammals are received. In particular, new experimental data about the importance guanine in 8-th position of the TATA-element for affinity to TBP are received. The experimental data, testifying that raised maintenance G and С nucleotides in flanks of TATA-element does the contribution to affinity to TBP are received.

Global distribution of negative cofactor 2 subunit-alpha on human promoters

Negative cofactor 2 (NC2) forms a stable complex with TATA-binding protein (TBP) on promoters in vitro. Its association with TBP prevents the binding of TFIIB and leads to inhibition of preinitiation complex formation. Here, we investigate the association of NC2 subunit-alpha with human RNA polymerase II promoter regions by using gene-specific ChIP and genome-wide promoter ChIPchip analyses. We find NC2alpha associated with a large number of human promoters, where it peaks close to the core regions. NC2 occupancy in vivo positively correlates with mRNA levels, which perhaps reflects its capacity to stabilize TBP on promoter regions. In single gene analyses, we confirm core promoter binding and in addition map the NC2 complex to enhancer proximal regions. High-occupancy histone genes display a stable NC2/TFIIB ratio during the cell cycle, which otherwise varies markedly from one gene to another. The latter is at least in part explained by an observed negative correlation of NC2 occupancy with the presence of the TFIIB recognition element in core promoter regions. Our data establish the genome-wide basis for general and gene-specific functions of NC2 in mammalian cells.

A facelift for the general transcription factor TFIIA

TFIIA was classified as a general transcription factor when it was first identified. Since then it has been debated to what extent it can actually be regarded as "general". The most notable feature of TFIIA is the proteolytical cleavage of the TFIIAalphabeta into a TFIIAalpha and TFIIAbeta moiety which has long remained a mystery. Recent studies have showed that TFIIA is cleaved by Taspase1 which was initially identified as the protease for the proto-oncogene MLL. Cleavage of TFIIA does not appear to serve as a step required for its activation as the uncleaved TFIIA in the Taspase1 knock-outs adequately support bulk transcription. Instead, cleavage of TFIIA seems to affect its turn-over and may be a part of an intricate degradation mechanism that allows fine-tuning of cellular levels of TFIIA. Cleavage might also be responsible for switching transcription program as the uncleaved and cleaved TFIIA might have distinct promoter specificity during development and differentiation. This review will focus on functional characteristics of TFIIA and discuss novel insights in the role of this elusive transcription factor.

Specific defects in different transcription complexes compensate for the requirement of the negative cofactor 2 repressor in Saccharomyces cerevisiae

Negative cofactor 2 (NC2) has been described as an essential and evolutionarily conserved transcriptional repressor, although in vitro and in vivo experiments suggest that it can function as both a positive and a negative effector of transcription. NC2 operates by interacting with the core promoter and components of the basal transcription machinery, like the TATA-binding protein (TBP). In this work, we have isolated mutants that suppress the growth defect caused by the depletion of NC2. We have identified mutations affecting components of three different complexes involved in the control of basal transcription: the mediator, TFIIH, and RNA pol II itself. Mutations in RNA pol II include both overexpression of truncated forms of the two largest subunits (Rpb1 and Rpb2) and reduced levels of these proteins. Suppression of NC2 depletion was also observed by reducing the amounts of the mediator essential components Nut2 and Med7, as well as by deleting any of the nonessential mediator components, except Med2, Med3, and Gal11 subunits. Interestingly, the Med2/Med3/Gal11 triad forms a submodule within the mediator tail. Our results support the existence of different components within the basic transcription complexes that antagonistically interact with the NC2 repressor and suggest that the correct balance between the activities of specific positive and negative components is essential for cell growth.

The general transcription machinery and general cofactors

In eukaryotes, the core promoter serves as a platform for the assembly of transcription preinitiation complex (PIC) that includes TFIIA, TFIIB, TFIID, TFIIE, TFIIF, TFIIH, and RNA polymerase II (pol II), which function collectively to specify the transcription start site. PIC formation usually begins with TFIID binding to the TATA box, initiator, and/or downstream promoter element (DPE) found in most core promoters, followed by the entry of other general transcription factors (GTFs) and pol II through either a sequential assembly or a preassembled pol II holoenzyme pathway. Formation of this promoter-bound complex is sufficient for a basal level of transcription. However, for activator-dependent (or regulated) transcription, general cofactors are often required to transmit regulatory signals between gene-specific activators and the general transcription machinery. Three classes of general cofactors, including TBP-associated factors (TAFs), Mediator, and upstream stimulatory activity (USA)-derived positive cofactors (PC1/PARP-1, PC2, PC3/DNA topoisomerase I, and PC4) and negative cofactor 1 (NC1/HMGB1), normally function independently or in combination to fine-tune the promoter activity in a gene-specific or cell-type-specific manner. In addition, other cofactors, such as TAF1, BTAF1, and negative cofactor 2 (NC2), can also modulate TBP or TFIID binding to the core promoter. In general, these cofactors are capable of repressing basal transcription when activators are absent and stimulating transcription in the presence of activators. Here we review the roles of these cofactors and GTFs, as well as TBP-related factors (TRFs), TAF-containing complexes (TFTC, SAGA, SLIK/SALSA, STAGA, and PRC1) and TAF variants, in pol II-mediated transcription, with emphasis on the events occurring after the chromatin has been remodeled but prior to the formation of the first phosphodiester bond.

Testifying the rice bacterial blight resistance gene xa5 by genetic complementation and further analyzing xa5 (Xa5) in comparison with its homolog TFIIAgamma1

The recessive gene xa5 for resistance to bacterial blight resistance of rice is located on chromosome 5, and evidence based on genetic recombination has been shown to encode a small subunit of the basal transcription factor IIA (Iyer and McCouch in MPMI 17(12):1348-1354, 2004). However, xa5 has not been demonstrated by a complementation test. In this study, we introduced the dominant allele Xa5 into a homozygous xa5-line, which was developed from a cross between IRBB5 (an indica variety with xa5) and Nipponbare (a japonica variety with Xa5). Transformation of Xa5 and subsequent segregation analysis confirmed that xa5 is a V39E substitution variant of the gene for TFIIAgamma on chromosome 5 (TFIIAgamma5 or Xa5). The rice has an addition gene for TFIIAgamma exists on chromosome 1 (TFIIAgamma1). Analysis of the expression patterns of Xa5 (TFIIAgamma5)/xa5 and TFIIAgamma1 revealed that both the genes are constitutively expressed in different rice organs. However, no expression of TFIIAgamma1 could be detected in the panicle by reverse transcriptase-polymerase chain reaction. To compare the structural difference between the Xa5/xa5 and TFIIAgamma1 proteins, 3-D structures were predicted using computer-aided modeling techniques. The modeled structures of Xa5 (xa5) and TFIIAgamma1 fit well with the structure of TFIIA small subunit from human, suggesting that they may all act as a small subunit of TFIIA. The E39V substitution in the xa5 protein occurs in the alpha-helix domain, a supposed conservative substitutable site, which should not affect the basal transcription function of TFIIAgamma. The structural analysis indicates that xa5 and Xa5 potentially retain their basic transcription factor function, which, in turn, may mediate the novel pathway for bacterial blight resistance and susceptibility, respectively.

Genetic analysis connects SLX5 and SLX8 to the SUMO pathway in Saccharomyces cerevisiae

MOT1 encodes an essential ATPase that functions as a general transcriptional regulator in vivo by modulating TATA-binding protein (TBP) DNA-binding activity. Although MOT1 was originally identified both biochemically and in several genetic screens as a transcriptional repressor, a combination of subsequent genetic, chromatin immunoprecipitation, and microarray analysis suggested that MOT1 might also have an additional role in vivo as a transcriptional activator. To better understand the role(s) of MOT1 in vivo, we selected for genomic suppressors of a mot1 temperature-sensitive mutation. This selection identified mutations in SPT15 (TBP) and BUR6, both of which are clearly linked with MOT1 at the functional level. The vast majority of the suppressor mutations, however, unexpectedly occurred in six genes that encode known components of the SUMO pathway and in two other genes with unknown functions, SLX5 and SLX8. Additional results presented here, including extensive synthetic lethality observed between slx5delta and slx8delta and SUMO pathway mutations, suggest that SLX5 and SLX8 are new components or regulators of the SUMO pathway and that SUMO modification might have a general role in transcriptional regulation as part of the TBP regulatory network.

Efficient Binding of NC2·TATA-binding Protein to DNA in the Absence of TATA

Negative cofactor 2 (NC2) forms a stable complex with TATA-binding protein (TBP) on promoters. This prevents the assembly of transcription factor (TF) IIA and TFIIB and leads to repression of RNA polymerase II transcription. Here we have revisited the interactions of NC2.TBP with DNA. We show that NC2.TBP complexes exhibit a significantly reduced preference for TATA box sequences compared with TBP and TBP.TFIIA complexes. In chromatin immunoprecipitations, NC2 is found on a variety of human TATA-containing and TATA-less promoters. Substantial amounts of NC2 are present in a complex with TBP in bulk chromatin. A complex of NC2.TBP displays a K(D) for DNA of approximately 2 x 10(-9) m for a 35-bp major late promoter oligonucleotide. While preferentially recognizing promoter-bound TBP, NC2 also accelerates TBP binding to promoters and stabilizes TBP.DNA complexes. Our data suggest that NC2 controls TBP binding and maintenance on DNA that is largely independent of a canonical TATA sequence.

NC2alpha interacts with BTAF1 and stimulates its ATP-dependent association with TATA-binding protein

Transcriptional activity of the TATA-binding protein (TBP) is controlled by a variety of proteins. The BTAF1 protein (formerly known as TAF(II)170/TAF-172 and the human ortholog of Saccharomyces cerevisiae Mot1p) and the NC2 complex composed of NC2alpha (DRAP1) and NC2beta (Dr1) are able to bind to TBP directly and regulate RNA polymerase II transcription both positively and negatively. Here, we present evidence that the NC2alpha subunit interacts with BTAF1. In contrast, the NC2beta subunit is not able to associate with BTAF1 and seems to interfere with the BTAF1-TBP interaction. Addition of NC2alpha or the NC2 complex can stimulate the ability of BTAF1 to interact with TBP. This function is dependent on the presence of ATP in cell extracts but does not involve the ATPase activity of BTAF1 nor phosphorylation of NC2alpha. Together, our results constitute the first evidence of the physical cooperation between BTAF1 and NC2alpha in TBP regulation and provide a framework to understand transcription functions of NC2alpha and NC2beta in vivo.