Sp family members and nuclear factor-Y cooperatively stimulate transcription from the rat pyruvate kinase M gene distal promoter region via their direct interactions

Transactivation of the progesterone receptor gene in granulosa cells: evidence that Sp1/Sp3 binding sites in the proximal promoter play a key role in luteinizing hormone inducibility

LH induction of the progesterone receptor (PR) in granulosa cells is a central event in ovulation. To identify critical regions of the mouse PR promoter that confer LH inducibility in granulosa cells, a mouse PR promoter (-384/+680) genomic fragment was ligated to a luciferase reporter construct and transfected into primary cultures of granulosa cells. Forskolin/phorbol myristate (PMA) induced PR promoter-luciferase reporter activity in granulosa cells greater than 15-fold. A deletion construct comprised only of the distal promoter alone (-348/+64) was inactive. Conversely, deletion constructs eliminating putative distal promoter-regulatory elements that bind Sp1, nuclear factor Y, and GATA-4 as well as the transcription start site (+1) failed to reduce forskolin/PMA activation of reporter activity. Additional 5'-deletions identified a minimal promoter region (+420/+680) sufficient to bestow cAMP responsiveness approximately 8- to 10-fold. Two GC-rich regions Sp1(A)[+440/+461] and Sp1(B) [+473/+490] bound Sp1/Sp3. Site-directed mutagenesis of Sp1(A) and Sp1(B) reduced activity of the proximal (+357/+680) promoter reporter construct approximately 50% and 99%, respectively. When the same Sp1(B) mutation was introduced into the intact promoter (-145/+680), forskolin/PMA induction of promoter activity was reduced by 70-80%. When the distal GC box as well as the proximal Sp1(B) site were both mutated in the context of the intact promoter, inducibility of the transgene was even more severely reduced. The importance of these Sp1/Sp3 binding regions was confirmed in human MCF-7 cells and Drosophila SL2 cells. Collectively, these results indicate that the Sp1/Sp3 binding sites within the mouse PR proximal promoter are essential for transactivation of the gene by agonists in granulosa cells. The molecular mechanisms by which LH activates Sp1/Sp3 at this region within the PR gene remain unknown but do not involve changes in the binding of Sp1/Sp3 to the critical GC boxes. Rather, Sp1/Sp3 appear to recruit other factors to the promoter.

Involvement of NF-Y and Sp1 binding sequences in basal transcription of the human telomerase RNA gene

The proximal promoter of the telomerase RNA gene, hTR, contains four Sp1 sites and one CCAAT box. We have carried out a functional analysis of the role of these sequence elements. Two Sp1 sites downstream of the CCAAT box mediated negative regulation, while the other two Sp1 sites were positive regulators with the strongest effect mediated by the negative regulatory Sp1 site closely flanking the CCAAT box. Basal transcriptional activity is maintained via the CCAAT box even when all four Sp1 sites are mutated, suggesting nuclear factor-Y (NF-Y) is a fundamental regulator of hTR promoter function. Chromatin immunoprecipitation revealed binding of NF-Y, Sp1 and TFIIB to the promoter in vivo. Thus the interaction of NF-Y at the CCAAT box is pivotal to hTR gene transcription and surrounding sequence elements may provide an environment for the regulation of activity through recruitment of additional protein complexes.

Genomic structure and analysis of transcriptional regulation of the mouse zinc-fingers and homeoboxes 1 (ZHX1) gene

The mouse zinc-fingers and homeoboxes 1 (ZHX1) gene was cloned and its transcriptional regulatory mechanism analysed. The mouse ZHX1 gene spans approximately 29 kb and consists of five exons. Exons 1-3 contain the nucleotide sequence of the 5'-noncoding region of mouse ZHX1 cDNA, exon 4 contains a part of the 5'-noncoding region, an entire coding sequence, and a part of the 3'-noncoding sequence, and exon 5 contains the resulting 3'-noncoding sequence. The ZHX1 gene exists as one copy in the haploid mouse genome. Two species of ZHX1 mRNA with or without the nucleotide sequence of the third exon are produced by an alternative splicing. To investigate the regulatory elements involved in the transcription of the ZHX1 gene, transient DNA transfection experiments with ZHX1/firefly luciferase reporter genes were performed using a lipofection method. Functional analyses of a series of 5'- and 3'-deletion constructs of the reporter genes revealed that the nucleotide sequence between -59 and +50 is required for full promoter activity in mouse embryonal carcinoma F9 cells. Two positive regulatory cis-acting elements in the region were identified. These elements, designated as Box A and Box B, are located between nucleotides -47 and -42 and +22 and +27, respectively, and synergistically stimulate transcription of the mouse ZHX1 gene. Electrophoretic mobility shift assays with specific competitors and antibodies show that PEA3 and Yin and Yang 1 (YY1) bind to Box A and Box B, respectively. Thus, we conclude that PEA3 and YY1 synergistically stimulate the transcription of the ZHX1 gene.

Transcriptional regulation of the epiregulin gene in the rat ovary

Ovarian follicular development is initiated by FSH secreted from the pituitary gland. The FSH-induced follicular development involves granulosa cell proliferation and differentiation. We demonstrated that a growth factor of epidermal growth factor (EGF) family epiregulin was rapidly induced in the primary culture of rat ovarian granulosa cells by FSH within 1 h. Epiregulin gene expression was also observed in granulosa cells of antral ovarian follicles from pregnant mare's serum gonadotropin-primed rats in vivo. To analyze the regulation of gene expression of epiregulin, we isolated and characterized the rat epiregulin gene of 22.1 kb, including 3.8 kb of 5'-upstream region as well as all five exons and four introns. We determined the transcriptional start site of rat epiregulin gene by primer extension analysis and then characterized the upstream promoter region of the gene. By using a luciferase reporter system, deletion and mutation analyses of rat epiregulin gene promoter region revealed that 125 bp upstream of transcriptional start site was essential, and that two CT boxes and one GT box within this region were important for the gene expression. We also demonstrated by EMSAs that Sp1/Sp3 proteins were involved in the epiregulin gene expression via the upstream sequence. Involvement of Sp1/Sp3 was also demonstrated that transfection of Sp1 or Sp3 expression plasmids dramatically increased the epiregulin gene promoter activities about 90- or 7.9-fold, respectively, in Drosophila SL2 cells that lack endogenous Sp family proteins. Such an increase in the promoter activity was also observed in mammalian cells when NIH-3T3 cells were used. In conclusion, we demonstrated here for the first time that EGF-type growth factor epiregulin is rapidly and strongly induced in the ovarian granulosa cells by FSH stimulation, and that two CT boxes and one GT box present in the upstream region are essential for the promoter activity of rat epiregulin. We also demonstrated that Sp family members play crucial roles in the epiregulin promoter activity through the CT boxes. The restricted and hormonally regulated expression of epiregulin in the rat ovarian granulosa cells may correspond to the physiological relevance of this peptide growth factor to the FSH-induced ovarian follicular growth and maturation.

Functional analysis and the molecular dissection of zinc-fingers and homeoboxes 1 (ZHX1)

Zinc-fingers and homeoboxes 1 (ZHX1) is a protein that interacts with the activation domain of the A subunit of nuclear factor-Y. The function of ZHX1, as a transcription factor, was characterized and their domains were mapped. To determine the nuclear localization signal, expression vectors, in which various truncated forms of ZHX1 were fused to the C-terminal of green fluorescence protein (GFP), were transfected into human embryonic kidney (HEK) 293 cells. All GFP-ZHX1 fusion proteins including an arginine-rich region that corresponds to the amino acid sequence between 734 and 768 were localized in the nuclei. A dimerization domain of the ZHX1 was also mapped using protein-protein interaction assays. The homeodomain (HD) 1 consisting of the amino acid sequence between 272 and 432 of ZHX1 was necessary and sufficient for dimerization. Lastly, the transcriptional activity of ZHX1 was examined using a mammalian one-hybrid system. ZHX1, fused to the C-terminal of the GAL4 DNA-binding domain, was co-transfected with luciferase reporter plasmids with or without five copies of the GAL4-binding site into HEK293 cells. The luciferase activity was decreased in both concentration- and GAL4-binding site-dependent manner. The acidic region corresponding to the amino acid sequence between 831 and 873 was a repressor domain and dimerization was prerequisited for full repressor activity.

Basal and parathyroid hormone induced expression of the human 25-hydroxyvitamin D 1alpha-hydroxylase gene promoter in kidney AOK-B50 cells: role of Sp1, Ets and CCAAT box protein binding sites

The regulation of the gene for renal 25-hydroxyvitamin D 1alpha- hydroxylase (1alpha(OH)ase; CYP27B1) by parathyroid hormone (PTH) under hypocalcemic conditions is fundamentally important for the maintenance of calcium and phosphate homeostasis. The molecular mechanism that underlies this hormonal response is of current interest and has been investigated in the present study by transfection analysis of the human 1alpha(OH)ase promoter in kidney AOK-B50 cells. We have shown that the first 305 bp of promoter can be induced by hormone in transient transfection assays and also within a chromatin environment when stably integrated. Mutagenesis of possible transcription factor binding sites within this promoter length has shown that three sites clustered within the region from -66 to -135 contribute to basal expression. A likely Sp1 and a CCAAT box site are particularly important for basal expression although these sites are not likely to functionally cooperate in a major way. Mutagenesis of the CCAAT box site consistently reduced PTH induction although mutagenesis of the Sp1, Ets and other possible binding sites in the 305 bp of promoter has no significant effect on the level of PTH induction. Other experiments showed that PTH induction but not basal expression was sensitive to the protein kinase inhibitor H89. We have therefore identified for the first time the sites in the 1alpha(OH)ase promoter responsible for basal expression and provide evidence for the role of a CCAAT box binding protein in a PTH mechanism of induction that involves an H89 sensitive step.

Rat zinc-fingers and homeoboxes 1 (ZHX1), a nuclear factor-YA-interacting nuclear protein, forms a homodimer

Zinc-fingers and homeoboxes 1 (ZHX1) is a protein which interacts with the activation domain of the A subunit of nuclear factor-Y. To analyze the physiological role(s) of ZHX1, we searched ZHX1-interacting protein(s) using a yeast two-hybrid system. The rat counterpart of ZHX1 cDNAs was cloned from an ovarian granulosa cell complementary DNA (cDNA) library, indicating that ZHX1 is able to form a homodimer. An analysis of the nucleotide sequence and its deduced amino acid sequence show that rat ZHX1 consists of 873 amino acid residues. Northern blot analysis shows that ZHX1 messenger RNA is expressed ubiquitously and that the level in the ovary are not regulated by gonadotropins. Furthermore, transfection experiments with green fluorescence protein (GFP) expression vectors into human embryonic kidney HEK293 cells reveal that full-length ZHX1 fused to the GFP is localized in the nuclei. Thus, we report on the molecular cloning, expression and characterization of full-length rat ZHX1 cDNA.

Transcription factors NF-Y and Sp1 are important determinants of the promoter activity of the bovine and human neuronal nicotinic receptor beta 4 subunit genes

The beta4 subunit is a component of the neuronal nicotinic acetylcholine receptors which control catecholamine secretion in bovine adrenomedullary chromaffin cells. The promoter of the gene coding for this subunit was characterized. A proximal region (from minus sign99 to minus sign64) was responsible for the transcriptional activity observed in chromaffin, C2C12, and COS cells. Within this region two cis-acting elements that bind transcription factors Sp1 and NF-Y were identified. Mutagenesis of the two elements indicated that they cooperate for the basal transcription activity of the promoter. The human beta4 promoter, that was also characterized, shared structural and functional homologies with the bovine promoter. Thus, two adjacent binding elements for Sp1 and NF-Y were detected. Whereas the Sp1 site was an important determinant of the promoter activity, the NF-Y site may have cell-specific effects. Given that these promoters showed no structural or functional homology with the previously characterized rat beta4 subunit promoter (Bigger, C. B., Casanova, E. A., and Gardner, P. D. (1996) J. Biol. Chem. 271, 32842--32848) except for the involvement of an Sp1 binding element, we propose that constitutive expression of the beta4 subunit gene in these three close species may be controlled by the general transcription factor Sp1. Nevertheless, other components could determine species-specific beta4 subunit expression.

Characterization of human cathepsin L promoter and identification of binding sites for NF-Y, Sp1 and Sp3 that are essential for its activity

Cathepsin L is a cysteine protease whose overexpression in human melanoma cells increases their tumorigenicity and switches their phenotype from non-metastatic to highly metastatic. Regulation of the transcription of the gene encoding human cathepsin L has not been yet studied and only preliminary data exist on the promoter regulation of the gene encoding rodent cathepsin L. In the present study we identified molecular elements involved in the transcriptional regulation of human cathepsin L in melanoma cells. The sequence of the 5'-flanking region of the gene encoding human cathepsin L was determined up to 3263 bp upstream of the translation start site. The major transcription intiation site was located. Three mRNA splice variants, differing in their 5' untranslated ends, were identified. Regulatory regions crucial for cathepsin L promoter activity were characterized between -1489 and -1646 bp. In this region, two GC boxes (-1590/-1595 and -1545/-1550) and a CCAAT motif (-1571/-1575) were involved in specific DNA-protein interactions. An electrophoretic mobility-shift assay demonstrated that Sp1 and Sp3 transcription factors bound to these GC boxes, and only the transcription factor nuclear factor Y (NF-Y) bound to the CCAAT motif. Mutagenesis studies demonstrated that these binding sites contributed at least 85% of cathepsin L promoter activity. Thus structural and functional analysis demonstrated that binding sites for NF-Y, Sp1 and Sp3 are essential for transcription of the gene encoding human cathepsin L in melanoma cells.

Transcriptional regulation of cell-specific expression of the human cystathionine beta -synthase gene by differential binding of Sp1/Sp3 to the -1b promoter

Cystathionine beta-synthase (CBS) catalyzes the condensation of serine and homocysteine to form cystathionine, an intermediate step in the synthesis of cysteine. We previously characterized the CBS -1b minimal promoter (-3792 to -3667) and found that Sp1/Sp3, nuclear factor Y, and USF-1 were involved in the regulation of basal promoter activity (Ge, Y., Konrad, M. A., Matherly, L. H., Taub, J. W. (2001) Biochem. J. 357, 97-105). In this study, the critical cis-elements and transcription factors in the CBS -1b upstream region (-4046 to -3792) were examined in HT1080 and HepG2 cells, which differ approximately 10-fold in levels of CBS transcripts transcribed from the CBS -1b promoter. In DNase I footprint and gel shift analyses and transient transfections of mutant CBS -1b promoter constructs into HT1080 and HepG2 cells, transcriptionally important roles for Sp1/Sp3 binding to three GC boxes and one GT box and for binding of myeloid zinc finger 1-like proteins to two myeloid zinc finger 1 elements were indicated. In gel shift assays, very low levels of Sp1/Sp3 DNA-protein complexes were detected in HT1080 cells compared with HepG2 cells despite comparable levels of nuclear factor Y and USF-1 binding and similar levels of Sp1 and Sp3 proteins on Western blots. Mixing of HT1080 and HepG2 nuclear extracts resulted in no difference in total Sp factor binding in gel shift assays, thus excluding a role for an unknown activator or inhibitor in the disparate Sp1/Sp3 binding between the lines. Increased Sp1/Sp3 binding in gel shift assays was observed upon treatment of HT1080 nuclear extracts with protein kinase A, and decreased Sp1/Sp3 binding resulted from treatment of HepG2 nuclear extracts with calf alkaline phosphatase, suggesting a role for changes in Sp1/Sp3 phosphorylation in transcription factor binding and transactivation of the CBS -1b promoter. Characterization of CBS promoter structure and function should clarify the molecular bases for variations in CBS gene expression in genetic diseases and the relationship between CBS and Down syndrome.

Induction of cPLA2 in lung epithelial cells and non-small cell lung cancer is mediated by Sp1 and c-Jun

Activating mutations in ras genes are frequently associated with non-small cell lung cancer cells (NSCLC) and contribute to transformed growth in these cells. Expression of oncogenic forms of Ras in these cells is associated with increased expression and activity of cytosolic phospholipase A(2) (cPLA(2)) and cyclooxygenase-2 (COX-2), leading to constitutively elevated levels of prostaglandin production. Expression of oncogenic Ras is sufficient to induce these enzymes in normal lung epithelial cells. We have previously reported that the JNK and ERK pathways are necessary for induction of cPLA(2) and have defined a minimal region of the cPLA(2) promoter from -58 to -12 that is required for Ha-Ras-mediated induction. To further characterize the cis-regulatory elements within this region involved in this response, site-directed mutagenesis was used to make mutations at various sites. Three cis-regulatory elements were identified: regions -21/-18, -37/-30, and -55/-53. Mutations in any of these elements decreased basal and Ha-Ras-induced cPLA(2) promoter activity in both normal lung epithelial cells, as well as steady state promoter activity in A549 cells, with a mutation in element -21/-18 completely eliminating all promoter activity. Overexpression studies and gel shift assays indicated that Sp1 may serve as a transcription factor functionally regulating promoter activity by directly interacting with two of the cis-regulatory elements, -21/-18 and -37/-30. Expression of Ha-Ras led to induction of c-Jun protein, which showed functional cooperation with Sp1 in driving promoter activity. Additional unidentified transcription factors bound to the regions from -55/-53 and -37/-34.

Transcriptional regulation of the murine acetyl-CoA synthetase 1 gene through multiple clustered binding sites for sterol regulatory element-binding proteins and a single neighboring site for Sp1

Cytosolic acetyl-CoA synthetase (AceCS1) activates acetate to supply the cells with acetyl-CoA for lipid synthesis. The cDNA for the mammalian AceCS1 has been isolated recently, and the mRNA was shown to be negatively regulated by sterols in cultured cells. In the current study, we describe the molecular mechanisms directing the sterol-regulated expression of murine AceCS1 by cloning and functional studies of the 5'-flanking region of the AceCS1 gene. An AceCS1 promoter-reporter gene (approximately 2.1 kilobase pairs) was negatively regulated when sterols were added to the medium of cultured cells, and the promoter was markedly induced by co-transfection of a plasmid that expresses the transcriptionally active nuclear form of either sterol regulatory element-binding protein (SREBP)-1a or -2 in HepG2 cells. Sequence analysis suggested that the AceCS1 promoter contains an E-box, two putative CCAAT-boxes, eight sterol regulatory element (SRE) motifs, and six GC-boxes. Gel shift assays demonstrated that all eight SRE motifs bound purified SREBP-1a in vitro with similar affinity. Luciferase reporter gene assays revealed that sterol regulation was critically dependent on three closely spaced SRE motifs and an adjacent GC-box. However, mutation of two putative upstream CCAAT-boxes did not affect SREBP dependent activation. Electrophoretic mobility "supershift" analyses confirmed that both Sp1 and Sp3 bound to the critical GC-box. In addition, transfection studies in Drosophila SL2 cells demonstrated that SREBP synergistically activated the AceCS1 promoter along with Sp1 or Sp3 but not with nuclear factor-Y.

Transcriptional regulation of the human cystathionine beta-synthase -1b basal promoter: synergistic transactivation by transcription factors NF-Y and Sp1/Sp3

Cystathionine beta-synthase (CBS) catalyses the condensation of serine and homocysteine to form cystathionine, an intermediate step in the synthesis of cysteine. Human CBS encodes five distinct 5' non-coding exons, the most frequent termed CBS -1a and CBS -1b, each transcribed from its own unique GC-rich TATA-less promoter. The minimal transcriptional region (-3792 to -3667) of the CBS -1b promoter was defined by 5'- and 3'-deletions, and transient transfections of reporter gene constructs in HepG2 cells, characterized by CBS transcription exclusively from the -1b promoter. Included in this 125 bp region are 3 GC-boxes (termed GC-a, GC-b and GC-c), an inverted CAAT-box and an E-box. By gel-shift and supershift assays, binding of specificity protein (Sp)1 and Sp3 to the GC-box elements, upstream stimulatory factor 1 (USF-1) to the E-box, and both nuclear factor (NF)-Y and an NF-1-like factor to the CAAT box could be demonstrated. By transient trans fections and reporter gene assays in HepG2 and Drosophila SL2 cells, a functional interplay was indicated between NF-Y binding to the CAAT-box, or between USF-1 binding to the E-box, and Sp1/Sp3 binding to the GC-box elements. In SL2 cells, NF-Y and Sp1/Sp3 were synergistic. Furthermore, both Sp1 and the long Sp3 isoform transactivated the CBS -1b minimal promoter; however, the short Sp3 isoforms were potent repressors. These results may explain the cell- or tissue-specific regulation of CBS transcription, and clarify the bases for alterations in CBS gene expression in human disease and Down's syndrome.

Organization and evolution of the human growth hormone receptor gene 5'-flanking region

Previous studies have identified eight variant human GH receptor (hGHR) messenger RNA (mRNAs; V1-V8), that differ in their 5'-untranslated regions (5'UTRs) but splice into the same site just upstream of the translation start site in exon 2; thus, they encode the same protein. Here we report a novel variant, V9, and describe the mapping of all nine 5'UTR sequences within 40 kb upstream of exon 2. A cluster of three sequences, V2-V9-V3 (termed module A), lies furthest 5', and approximately 16 kb downstream is a second cluster of four exons, V7-V1-V4-V8 (module B). V6 is midway between modules A and B. Module B is about 18 kb upstream of V5, which lies adjacent to exon 2. hGHR expression is under developmental- and tissue-specific regulation, and expression of the variant mRNAs is related to their position within the 5'-flanking region; whereas module A (V2,V9,V3) and V5 variants are widely expressed, module B (V7,V1,V4,V8) and V6 variant mRNAs are detectable only in postnatal liver. Transcriptional start sites for V1 and V9 (representing the two different modules) were identified, showing that postnatal liver-specific expression of V1 is driven from two TATA boxes, whereas the ubiquitous V9 transcript has a single start site and a TATA-less promoter. V9 promoter activity was shown by in vivo and in vitro transfection assays, and an NF-Y binding site was demonstrated by electromobility shift assay. Thus, the regulatory regions of the hGHR gene are complex, and the clustering of seven 5'UTR exons within two modules with distinctly different mRNA expression patterns is the most striking feature.

Cloning and functional expression of an E box-binding protein from rat granulosa cells

Ovarian granulosa cells undergo cell growth and cytodifferentiation during follicular maturation. In a number of tissues, the gene expression that is responsible for the cytodifferentiation is largely dependent on E box(es) located upstream of the responsible genes. In this study, we report on the cloning of cDNA(s) encoding E box (5'-CACGTG-3')-binding protein from a rat granulosa cell cDNA library using a yeast one-hybrid system. When multiple E box sequences were used as target, we obtained a positive clone that encodes the rat homologue of upstream stimulatory factor 2 (USF2). An analysis of the nucleotide sequence and its deduced amino acid sequence reveals that rat USF2 protein consists of 346 amino acid residues and belongs to the basic helix-loop-helix/leucine zipper protein family. Northern blot analysis shows that rat USF2 mRNA exists as multiple forms between 1.6 and 2.2 kilobases. The size of the cloned insert was identical to that of the transcript of maximal length. Electrophoretic mobility shift assays showed that in vitro-translated rat USF2 specifically binds to the E box. In addition, cotransfection experiments with luciferase-reporter constructs in HepG2 cells reveal that the overexpression of rat USF2 leads to an increase of luciferase activity in the E box sequence-dependent manner. Thus, we report molecular cloning, expression, and functional characterization of full-length rat USF2 cDNA.

NF-Y binding is required for transactivation of neuronal aromatic L-amino acid decarboxylase gene promoter by the POU-domain protein Brn-2

We have previously characterized binding sites for the NF-Y transcription factor (-71/-52) and Brn-2 POU-domain protein (-92/-71) in the neuronal promoter of the human aromatic L-amino acid decarboxylase gene [Mol. Brain Res. 56 (1998) 227]. We have now explored the functional role of these binding sites in transfected SK-N-BE neuroblastoma cells. Mutations of the NF-Y site that abolish binding depressed expression of a luciferase reporter gene up to 25-fold. The overexpression of a dominant negative mutant of NF-YA subunit depressed expression by 60%. Promoter activity was increased by the overexpression of Brn-2. Mutations or deletion of the binding site of Brn-2 did not suppress transcriptional activation by overexpressed Brn-2, while promoters defective in NF-Y binding were not transactivated by Brn-2. A GST-pulldown experiment showed that recombinant human Brn-2 protein weakly interacts with recombinant NF-Y outside of DNA. Cooperative binding of recombinant NF-Y and GST--Brn-2 proteins on the neuronal promoter was evidenced by an electrophoretic mobility shift assay. The POU-domain of Brn-2 was sufficient for such interaction. The results thus suggest that the activation of the neuronal promoter of the aromatic L-amino acid decarboxylase gene requires a direct interaction between the ubiquitous NF-Y factor and a cell-specific POU-domain protein. The NF-Y, but not the Brn-2 binding site, is essential for the recruitment of the NF-Y/Brn-2 complex on the promoter.