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Down-regulation by cAMP of angiotensin II type 2 receptor gene expression in PC12 cells.

The rat angiotensin II type 2 receptor (AT2-R) gene was isolated, and cis-regulatory regions in its 5'-flanking area were analyzed. Primer extension and RNase protection analyses revealed a single transcriptional initiation site at the position 24 bp downstream of the TATA box. The 5'-flanking region of AT2-R contained several cis-regulatory elements, such as AP-1, AP-2, C/EBP, NF-1, NF-IL6, NF-kappa B, and glucocorticoid- and cAMP-responsive elements (CRE). The treatment of PC12 cells with dibutyryl cAMP caused a marked decrease (90%) in the AT2-R mRNA level, which was blocked by the inhibitor of protein kinase A and did not require new protein synthesis. The protein level was also reduced 84% after a 24-h exposure to cAMP and the binding affinity was unchanged. The half-life of the AT2-R mRNA decreased -66% by cAMP as compared with control (18.4 +/- 0.4 h). Deletion and mutation analyses of the 5'-flanking region (1.2 Kb) revealed that there were one negative (-1,199 to -739) and two positive cis-regulatory regions (-739 to -436 and -59 to +45), and that the CRE motif located at -426 repressed (-23%) the promoter activity of the rat AT2-R gene. The region between -59 and +45 containing TATA box and AP-2 site accounted for 70% of the promoter activity. These findings indicate that the promoter activity of the rat AT2-R gene is modulated by several cis-regulatory regions and that cAMP markedly downregulates the expression of the AT2-R mainly by inducing AT2-R mRNA destabilization rather than CRE-mediated inhibition of the gene transcription. Thus, humoral factors that transduce cAMP as an intracellular signal may modulate AT2-R-mediated function of Ang II by reducing AT2-R expression.

Animals↗

Cellular repressor inhibits human cytomegalovirus transcription from the UL127 promoter.

The region of the human cytomegalovirus (HCMV) genome between the UL127 promoter and the major immediate-early (MIE) enhancer is referred to as the unique region. The role of this region during a viral infection is not known. In wild-type HCMV-infected permissive fibroblasts, there is no transcription from the UL127 promoter at any time during productive infection. Our investigators previously reported that the region upstream of the UL127 TATA box repressed expression from the UL127 promoter (C. A. Lundquist et al., J. Virol. 73:9039-9052, 1999). The region was reported to contain functional NF1 DNA binding sites (L. Hennighausen and B. Fleckenstein, EMBO J. 5:1367-1371, 1986). Sequence analysis of this region detected additional consensus binding sites for three transcriptional regulatory proteins, FoxA (HNF-3), suppressor of Hairy wing, and CAAT displacement protein. The cis-acting elements in the unique region prevented activation of the early UL127 promoter by the HCMV MIE proteins. In contrast, deletion of the region permitted very high activation of the UL127 promoter by the viral MIE proteins. Mutation of the NF1 sites had no effect on the basal activity of the promoter. To determine the role of the other sites in the context of the viral genome, recombinant viruses were generated in which each putative repressor site was mutated and the effect on the UL127 promoter was analyzed. Mutation of the putative Fox-like site resulted in a significant increase in expression from the viral early UL127 promoter. Insertion of wild-type Fox-like sites between the HCMV immediate-early (IE) US3 TATA box and the upstream NF-kappaB-responsive enhancer (R2) also significantly decreased gene expression, but mutated Fox-like sites did not. The wild-type Fox-like site inhibits activation of a viral IE enhancer-containing promoter. Cellular protein, which is present in uninfected or infected permissive cell nuclear extracts, binds to the wild-type Fox-like site but not to mutated sites. Reasons for repression of UL127 gene transcription during productive infection are discussed.

Base Sequence↗

Limited bidirectional activity of two housekeeping gene promoters: human HPRT and PGK.

Typical of other housekeeping genes, the promoter for the human hypoxanthine phosphoribosyl transferase-encoding gene (HPRT) is G + C-rich, lacks a TATA box and has multiple transcription start points. To test the hypothesis that these features may result in relaxed control over the direction of transcription, we examined the effect of orientation on the ability of the HPRT promoter to control expression of the following reporter genes in transfected cells: luc (firefly luciferase), cat (bacterial chloramphenicol acetyltransferase) and neo (neomycin resistance). A 376-bp fragment containing the HPRT promoter efficiently expressed the luc gene irrespective of orientation, and the 5' ends of luciferase RNA produced in cells transfected with inverted promoter constructs mapped to within the HPRT promoter, indicating that the HPRT promoter has bidirectional activity. However, in the presence of two divergently-flanking reporter genes expression from the inverted HPRT promoter was only 10-20% compared to the noninverted orientation. Furthermore, the inverted HPRT promoter expressed cat less well than luc, and was unable to express neo sufficiently well to produce any colonies under appropriate selection conditions. Attempts to detect endogenous divergent HPRT transcripts were unsuccessful. The promoter of another housekeeping gene, encoding 3-phosphoglycerate kinase (PGK), expressed moderate levels of cat (40%) but not luc (less than 5%) in the inverted orientation. By comparison, two TATA-box containing promoters functioned extremely poorly when inverted. This study indicates that two plasmid-borne housekeeping promoters have at least a limited potential for bidirectional activity, but the functional significance of this is unclear if the corresponding endogenous housekeeping promoters express divergent transcripts at similarly low levels. The poor activity of the HPRT and PGK promoters in the inverted orientation suggests that there is a mechanism which influences the direction of transcription from these promoters.

Chloramphenicol O-Acetyltransferase↗

Transcription factor Oct-2A contains functionally redundant activating domains and works selectively from a promoter but not from a remote enhancer position in non-lymphoid (HeLa) cells.

In non-lymphoid cells such as HeLa cells, ectopic expression of the lymphocyte-specific transcription factor Oct-2A can activate reporter genes whose promoters consist of a single octamer sequence (ATTTGCAT) upstream of a TATA box. While the factor is strongly active in a promoter position, it tails as an enhancer factor: an enhancer consisting of multiple copies of the octamer sequence placed downstream of the reporter gene is not active in HeLa cells, even at high concentration of Oct-2A. In B lymphoid cells, however, the same enhancer is highly active. This could mean that an additional factor is required for enhancer activation in B cells. Furthermore, we have tested the transcriptional activation potential of Oct-2A with a series of N-terminal and C-terminal deletions. We show that a glutamine-rich domain near the N-terminus is required for full activity. Otherwise, large segments of the N-terminal half or the entire C-terminal region are dispensable in our assay, as long as the deletions do not impinge on the conserved POU domain which is sufficient for DNA binding. While N-terminal and C-terminal regions can functionally compensate for each other, a combined deletion that only retains the POU domain is a strong down mutation. We also find that activity depends on the promoter structure of the reporter gene: the POU domain by itself shows some activity with a promoter where the octamer sequence is located very close to the TATA box, but no activity with another promoter construction where the octamer sequence is located further upstream. The two promoters also respond differently to the deletion of the glutamine-rich stretch important for transcriptional activation. From these experiments we consider it likely that the natural octamer factor variants can selectively activate the different naturally occurring octamer-containing promoters.

Amino Acid Sequence↗

Different TBP-associated factors are required for mediating the stimulation of transcription in vitro by the acidic transactivator GAL-VP16 and the two nonacidic activation functions of the estrogen receptor.

The estrogen receptor (ER) contains two nonacidic transcriptional activation functions, AF-1 and AF-2 (formerly TAF-1 and TAF-2). In this study we show that AF-1 and AF-2 are able to stimulate transcription in vitro in a HeLa cell system when fused to the DNA binding domain of the yeast activator GAL4. We also demonstrate that a factor(s) required for the function of the ER AFs is chromatographically separable from a factor(s) necessary for the activity of the acidic activation domain of VP16. Moreover, immunoprecipitation experiments using a monoclonal antibody directed against the TATA box binding protein (TBP) indicate, that these different factors are associated with TBP in distinct TFIID complexes.

Amino Acid Sequence↗

The retinoblastoma protein binds E2F residues required for activation in vivo and TBP binding in vitro.

The retinoblastoma (RB) tumour suppressor protein is capable of repressing the activity of promoters containing DNA binding sites for the transcription factor E2F. Recently a protein which binds RB and possesses the DNA binding characteristics of E2F has been cloned. Here we show that the E2F activation domain is the target for RB-induced repression. RB can silence the 57 residue E2F activation domain but cannot effectively repress an E2F mutant which has reduced RB binding capacity. Extensive mutagenesis of E2F shows residues involved in RB binding are required for transcription activation. Mutations which affect both functions most dramatically lie within the minimal RB binding region. A further subset of sensitive residues lies within a new repeat motif E/DF XX L X P which flanks the minimum RB binding site. These data show that RB can mask E2F residues involved in the activation process, possibly by mimicking a component of the transcriptional machinery. Consistent with this model, we find that the TATA box binding protein TBP can bind to the E2F activation domain in vitro in a manner indistinguishable from that of RB.

Amino Acid Sequence↗

Interaction between the Arabidopsis thaliana heat shock transcription factor HSF1 and the TATA binding protein TBP.

The heat shock factor (HSF1) is the central regulator of the heat stress (hs) response and is required for stimulating the transcription of the hs genes and consequently the expression of heat shock proteins. To promote the polymerase II-dependent transcription of the hs genes, HSF has to communicate with the basal transcription machinery. Here, we report that the Arabidopsis thaliana HSF1 interacts directly with TBP, the general TATA box binding transcription factor, as shown by affinity chromatography and electrophoretic mobility shift analyses in vitro. An in vivo interaction between AtHSF1 and AtTBP1 was suggested by results employing the yeast two-hybrid system.

Arabidopsis↗

Simultaneous binding and bending of promoter DNA by the TATA binding protein: real time kinetic measurements.

The binding and bending of tetramethylrhodamine-5'-(GGGCTATAAAAGGG) duplex-3'-fluorescein by native Saccharomyces cerevisiae TATA binding protein (TBP) have been investigated using fluorescence resonance energy transfer. Probability distributions derived from fluorescein emission lifetime measurements show a decrease in the mean 3'-fluorescein-5'- rhodamine distance from 56.5 to 46.8 A upon binding of the oligomer to TBP, consistent with the DNA bend observed by X-ray crystallography. The kinetics, monitored in real time using stopped flow fluorimetry, demonstrate simultaneous binding and bending of a TATA box by TBP with a single second-order rate constant of (2.4 +/- 0.3) x 10(6) M-1 s-1 at 30 degrees C.

Base Sequence↗

Biochemistry and structural biology of transcription factor IID (TFIID).

Eukaryotes have three distinct RNA polymerases that catalyze transcription of nuclear genes. RNA polymerase II is responsible for transcribing nuclear genes encoding the messenger RNAs and several small nuclear RNAs. Like RNA polymerases I and III, pol II cannot recognize its target promoter directly and initiate transcription without accessory factors. Instead, this large multisubunit enzyme relies on both general transcription factors and transcriptional activators and coactivators to regulate transcription from class II promoters. At the center of this process is TFIID, a 700-kD complex composed of the TATA box binding protein (TBP) and a set of phylogenetically conserved, polymerase-specific TBP-associated factors or TAFIIS. Together, TBP and the TAFIIS direct assembly of the transcription machinery and play critical regulatory roles in eukaryotic gene expression.

Amino Acid Sequence↗

Coactivator and promoter-selective properties of RNA polymerase I TAFs.

Human ribosomal RNA synthesis by RNA polymerase I requires the activator UBF and the promoter selectivity factor SL1, which consists of the TATA binding protein (TBP) and three associated subunits, TAFI110, TAFI63, and TAFI48. Here it is shown that both TAFI110 and TAFI63 contact the promoter, whereas TAFI48 serves as a target for interaction with UBF and is required to form a transcriptionally active SL1 complex responsive to UBF in vitro. TAFI48 also alters the ability of TBP to interact with TATA box elements, and the resulting complex fails to support transcription by RNA polymerase II. Thus, TAFI48 may function both as a target to mediate UBF activation and as a class-specific promoter selectivity factor.

DNA-Binding Proteins↗

Crystal structure of the yeast TFIIA/TBP/DNA complex.

The crystal structure of the yeast TFIIA/TBP/TATA promoter complex was solved to 3 angstrom resolution by double-edge multiple wavelength anomalous diffraction from two different species of anomalous scattering elements in the same crystal. The large and small subunits of TFIIA associate intimately to form both domains of a two-domain folding pattern. TFIIA binds as a heterodimer to the side of the TBP/TATA complex opposite to the side that binds TFIIB and does not alter the TBP/DNA interaction. The six-stranded beta-sandwich domain interacts with the amino-terminal end of TBP through a stereospecific parallel beta-strand interface and with the backbone of the TATA box and the 5'-flanking B-DNA segment. The four-helix-bundle domain projects away from the TBP/TATA complex, thereby presenting a substantial surface for further protein-protein interactions.

Amino Acid Sequence↗

Multiple characteristics of a pentameric regulatory array endow the human alpha-subunit glycoprotein hormone promoter with trophoblast specificity and maximal activity.

Trophoblast-specific expression of the human alpha-subunit glycoprotein hormone gene requires a tightly linked array of five different regulatory elements [trophoblast-specific element (TSE), alpha-activating element (alphaACT), a tandem cAMP response element (CRE), junctional regulatory element (JRE), and a CCAAT box]. We examined their contextual contributions to trophoblast-specific expression by using transfection assays to evaluate activity of systematic block replacement mutations made within the 1500-bp 5'-flanking region of the human alpha-subunit gene. While all five elements were required for full activity, only the TSE and JRE displayed trophoblast specificity. Interestingly, the TSE-binding protein has limited tissue distribution whereas a JRE-binding protein appears trophoblast specific. Likewise, replacement studies with an AP-1 element that binds heterodimers of jun and fos indicated that this element was incapable of compensating for either the tandem CRE or JRE. This preference for both CRE- and JRE-binding proteins provides another avenue for configuring an alpha-subunit promoter with trophoblast specificity. Additional analysis with a cAMP response element binding protein (CREB)-Gal4 fusion protein further underscored the importance of CREB as well as suggested that transcriptional contributions come from both the DNA-binding domain and transactivation domain of this protein. We also examined the interactive nature of the pentameric array by placing a 15-bp random sequence between each element. Remarkably, only the insertion 3' of the CCAAT box diminished promoter activity. This suggested the absence of direct interactions between the transcriptional factors that bind each element in the array. It also suggested that the CCAAT box is position-dependent relative to the TATA box. This position dependence appeared cell-specific, as it was not manifest in a gonadotrope cell line (alphaT3-1 cells). Thus, the CCAAT box also has tissue-specific characteristics that assist in targeting expression of the alpha-subunit gene to trophoblasts. Together, these data suggest that multiple characteristics of a complex pentameric array of regulatory elements endow the alpha-subunit promoter with trophoblast specificity and maximal activity.

Cyclic AMP Response Element-Binding Protein↗

Biochemical characterization of the TATA-binding protein-Gal4 activation domain complex.

It has been suggested that complexes between gene-specific activators and the TATA-binding protein (TBP) play an important role in the expression of many genes. However, few detailed studies of well defined activator-TBP complexes have been reported. An analysis of the biochemical properties of the complex formed by the acidic activation domain (AAD) of the yeast activator Gal4 and TBP is presented here. This is shown to be composed of two AAD and one TBP molecule. DNA binding experiments reveal that TATA-containing DNAs and the Gal4 AAD bind TBP competitively, suggesting that the AAD and TATA boxes recognize overlapping surfaces of TBP. The kinetics of the formation and dissociation of the AAD(2)-TBP complex is also probed. The impact of these findings on models for Gal4-mediated transcriptional activation is considered.

Binding, Competitive↗

Effects of phosphorylation by protein kinase CK2 on the human basal components of the RNA polymerase II transcription machinery.

We have investigated the role of phosphorylation by vertebrate protein kinase CK2 on the activity of the General Transcription Factors TFIIA, TFIIE, TFIIF, and RNAPII. The largest subunits of TFIIA, TFIIE, and TFIIF were phosphorylated by CK2 holoenzyme. Also, RNA polymerase II was phosphorylated by CK2 in the 214,000 and 20,500 daltons subunits. Our results show that phosphorylation of TFIIA, TFIIF, and RNAPII increase the formation of complexes on the TATA box of the Ad-MLP promoter. Also, phosphorylation of TFIIF increases the formation of transcripts, where as phosphorylation of RNA polymerase II dramatically inhibits transcript formation. Furthermore, we demonstrate that CK2 beta directly interacts with RNA polymerase II, TFIIA, TFIIF, and TBP. These results strongly suggest that CK2 may play a role in regulating transcription of protein coding genes.

Adenoviridae↗

The human Nramp2 gene: characterization of the gene structure, alternative splicing, promoter region and polymorphisms.

Nramp2 is a gene encoding a transmembrane protein that is important in metal transport, in particular iron. Mutations in nramp2 have been shown to be associated with microcytic anemia in mk/mk mice and defective iron transport in Belgrade rats. Nramp2 contains a classical iron responsive element in the 3' untranslated region that confers iron dependent mRNA stabilization. In this report, we describe a splice variant form of human nramp2 that has the carboxyl terminal 18 amino acids substituted with 25 novel amino acids and has a new 3' untranslated region lacking a classical iron-responsive element. This splice form of nramp2, nramp2 non-IRE, was found to be derived from splicing of an additional exon into the terminal coding exon. The nramp2 gene is comprised of 17 exons and spans more than 36 kb. It contains an additional 5' exon and intron (exon and intron 1) and an additional 3' exon (exon 17) and intron (intron 16) as compared to nramp1, a homologous gene. The additional exons and introns account for much of the difference in length between nramp2 (> 36 kb) and nramp1 (12 kb). The exon-intron borders of nramp2 exons 3-15 are homologous to nramp1 exons 2-14. The nramp2 5' regulatory region contains two CCAAT boxes but lacks a TATA box. The 5' regulatory region of nramp2 also contains five potential metal response elements (MRE's) that are similar to the MRE's found in the metallothionein-IIA gene, three potential SP1 binding sites and a single gamma-interferon regulatory element. Five single nucleotide mutations or polymorphisms were identified within the nramp2 gene. One of these, 1303C-->A, occurs in the coding region of nramp2 and results in an amino acid change from leucine to isolecine. A polymorphism, 1254T/C, also occurs in the coding region of nramp2 but does not cause an amino acid change. The other 3 polymorphisms are within introns (IVS2 + 11A/G, IVS4 + 44C/A, and IVS6 + 538G/Gdel). In addition, a polymorphic microsatellite TATATCTATATATC (TA)6-7 (CA)10-11 CCCCCTATA (TATC)3 (TCTG)5 TCCG (TCTA)6 was identified in intron 3. Analysis of cDNA derived by direct amplification of reversed transcribed RNA or cDNA clones isolated from a library provide evidence of skipping of exons 10 and 12 of nramp2. Deletion of either of these exons would result in a sequence that remains in frame yet would generate a protein that would lack transmembrane spanning region 7 or 8 respectively. The deletion of a single transmembrane domain would have severe topological consequences. The coding region of the nramp2 gene of hemochromatosis patients with or without mutations in the hemochromatosis gene, HFE, were examined and found to be normal. One hemochromatosis patient, with a normal HFE genotype, was heterozygous for the 1303C-->A mutation. Furthermore, in an examination of hemochromatosis patients with mutant HFE and normal HFE genes, we did not observe a linkage disequilibrium of either group with a particular nramp2 haplotype. These data suggest that mutations in nramp2 are not commonly associated with hemochromatosis.

Amino Acid Sequence↗

Genomic organization of the human beta-catenin gene (CTNNB1).

The cytoplasmic beta-catenin protein is implicated in signal transduction and associates with both the cell-cell adhesion protein E-cadherin and the tumor suppressor gene product APC. We determined the primary structure of the human beta-catenin gene (CTNNB1) by analysis of cDNA and genomic clones. The size of the complete gene was determined to be 23.2 kb. Restriction mapping and partial sequence analysis revealed 16 exons. All splice donor and acceptor sites were conformable to the GT/AG rule. The exon size ranged from 61 to 790 bp. Half of the introns were smaller than 550 bp, with the smallest being 84 bp and the longest being 6700 bp. The intron-exon boundaries did not coincide either with conserved sites in the 12 armadillo repeat sequences of beta-catenin or with intron-exon boundaries in the armadillo gene of Drosophila. A major site for transcription initiation was identified as an A residue 214 nucleotides upstream of the ATG initiation codon. The resulting transcript is 3362 nucleotides long. Compared to the previously published mRNA sequence, additional residues were identified, 16 at the 5' end and 766 at the 3' end of the mRNA. An alternative splice acceptor site within exon 16 reduced the 3' UTR sequence by 159 bp. Polymerase chain reaction on cDNA from 14 human cell lines demonstrated the general occurrence of both splice variants. The 5'-flanking region is highly GC-rich and lacks a CCAAT box, but contains a TATA box and potential binding sites for several transcription factors, such as NF kappa B, SP1, AP2, and EGR1. Both a 437-bp fragment and a 6-kb fragment, containing about 4.7 kb of the 5'-flanking region in addition to the noncoding exon 1 and 1 kb of intron 1, showed clear promoter activity when these fragments were linked to a secreted alkaline phosphatase reporter gene and transfected into a mouse epithelial cell line.

Alternative Splicing↗

Genomic organization, promoter analysis, and chromosomal localization of the gene for the mouse glial high-affinity glutamate transporter Slc1a3.

The mouse gene encoding glial high-affinity, Na+-dependent glutamate transporter Slc1a3 (GluT-1/GLAST) was isolated, and its structural organization was characterized. The gene appeared to exist as a single copy in the mouse genome and comprised 10 exons spanning more than 56 kilobases. The transcription initiation sites were mapped to positions 503, which is the first transcriptional point (defined as +1), 128 (+376), and 64 (+440) basepairs upstream of the 3'-end of exon 1 by primer extension. The 5'-flanking region of the mouse GluT-1 gene had a typical CCAAT box and a GC box but lacked a TATA box. These features of the promoter region were characteristic of housekeeping genes. The fusion plasmids containing approximately 4 kb of the 5'-flanking region (-3830 to +450) and the firefly luciferase gene induced a significant luciferase activity when transfected into COS-1 cells. Distal deletion of the 5'-flanking region, leaving 619 bp (-169 to +450), resulted in a marked decrease in luciferase activity in COS-1 cells, suggesting that a CCAAT box, which was positioned at -200, is necessary for the expression of this gene. In situ hybridization localized this gene to mouse chromosome 15A2. These structural features will lead to a better understanding of the regulatory mechanism of the expression of the GluT-1 gene by ischemia and will also provide a basis for future evolutionary comparisons with other neurotransmitter transporters.

ATP-Binding Cassette Transporters↗