Synergistic transcriptional activation by Sox10 and Sp1 family members

Positive autoregulation of Sox17 is necessary for gallbladder and extrahepatic bile duct formation

Expression of SRY-box transcription factor 17 (Sox17) in the endodermal region caudal to the hepatic diverticulum during late gastrulation is necessary for hepato-pancreato-biliary system formation. Analysis of an allelic series of promoter-proximal mutations near the transcription start site (TSS) 2 of Sox17 in mouse has revealed that gallbladder (GB) and extrahepatic bile duct (EHBD) development is exquisitely sensitive to Sox17 expression levels. Deletion of a SOX17-binding cis-regulatory element in the TSS2 promoter impairs GB and EHBD development by reducing outgrowth of the nascent biliary bud. These findings reveal the existence of a SOX17-dependent autoregulatory loop that drives Sox17 expression above a critical threshold concentration necessary for GB and EHBD development to occur, and that minor impairments in Sox17 gene expression are sufficient to impair the expression of SOX17-regulated genes in the nascent GB and EHBD system, impairing or preventing development.

Nicotine-induced expression of low-density lipoprotein receptor in oral epithelial cells

Background

Nicotine use is one of the most important risk factors for the development of cardiovascular and periodontal diseases. Numerous reports have suggested the possible contribution of disturbed lipid metabolism for the development of both disease groups. Despite these observations, little is known about the relationship between tobacco smoking and the development of these diseases. Our previous microarray data revealed that nicotine induced low-density lipoprotein receptor (LDLR) expression in oral epithelial cells (OECs). The aim of the present study was to confirm nicotine-mediated LDLR induction and to elucidate the signaling mechanisms leading to the augmented expression of LDLR in OECs.

Methods and Results

LDLR and nicotinic acetylcholine receptor (nAChR) subunit expression was detected by real-time PCR. The production of LDLR was demonstrated by immunofluorescence staining. nAChR-mediated LDLR induction was examined by pre-incubation of the cells with its specific inhibitor, α-bungarotoxin (α-BTX). The functional importance of transcription factor specific protein 1 (Sp1) was examined by luciferase assay, mithramycin pre-incubation or by small interfering RNA (siRNA) transfection. The specific binding of Sp1 to R3 region of LDLR 5’-untranslated region was demonstrated with electrophoretic mobility shift assay (EMSA) and streptavidin-agarose precipitation assay followed by western blotting. The results confirmed that nicotine induced LDLR expression at the transcriptional level. Nicotine was sensed by nAChR and the signal was transduced by Sp1 which bound to the R3 region of LDLR gene. Augmented production of LDLR in the gingival epithelial cells was further demonstrated by immunofluorescence staining using the gingival tissues obtained from the smoking patients.

Conclusions

Taken together, the results suggested that nicotine might contribute to the development of both cardiovascular and periodontal diseases by inducing the LDLR in OECs thereby disturbing lipid metabolism.

The MADS box transcription factor MEF2C regulates melanocyte development and is a direct transcriptional target and partner of SOX10

Waardenburg syndromes are characterized by pigmentation and autosensory hearing defects, and mutations in genes encoding transcription factors that control neural crest specification and differentiation are often associated with Waardenburg and related disorders. For example, mutations in SOX10 result in a severe form of Waardenburg syndrome, Type IV, also known as Waardenburg-Hirschsprung disease, characterized by pigmentation and other neural crest defects, including defective innervation of the gut. SOX10 controls neural crest development through interactions with other transcription factors. The MADS box transcription factor MEF2C is an important regulator of brain, skeleton, lymphocyte and cardiovascular development and is required in the neural crest for craniofacial development. Here, we establish a novel role for MEF2C in melanocyte development. Inactivation of Mef2c in the neural crest of mice results in reduced expression of melanocyte genes during development and a significant loss of pigmentation at birth due to defective differentiation and reduced abundance of melanocytes. We identify a transcriptional enhancer of Mef2c that directs expression to the neural crest and its derivatives, including melanocytes, in transgenic mouse embryos. This novel Mef2c neural crest enhancer contains three functional SOX binding sites and a single essential MEF2 site. We demonstrate that Mef2c is a direct transcriptional target of SOX10 and MEF2 via this evolutionarily conserved enhancer. Furthermore, we show that SOX10 and MEF2C physically interact and function cooperatively to activate the Mef2c gene in a feed-forward transcriptional circuit, suggesting that MEF2C might serve as a potentiator of the transcriptional pathways affected in Waardenburg syndromes.

From smoking to lung cancer: the CHRNA5/A3/B4 connection

Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels that modulate key physiological processes ranging from neurotransmission to cancer signaling. These receptors are activated by the neurotransmitter, acetylcholine, and the tobacco alkaloid, nicotine. Recently, the gene cluster encoding the alpha3, alpha5 and beta4 nAChR subunits received heightened interest after a succession of linkage analyses and association studies identified multiple single-nucleotide polymorphisms in these genes that are associated with an increased risk for nicotine dependence and lung cancer. It is not clear whether the risk for lung cancer is direct or an effect of nicotine dependence, as evidence for both scenarios exist. In this study, we summarize the body of work implicating nAChRs in the pathogenesis of lung cancer, with special focus on the clustered nAChR subunits and their emerging role in this disease state.

A transcriptional regulatory element critical for CHRNB4 promoter activity in vivo

Genome-wide association studies have underscored the importance of the clustered neuronal nicotinic acetylcholine receptor (nAChR) subunit genes with respect to nicotine dependence as well as lung cancer susceptibility. CHRNB4, which encodes the nAChR β4 subunit, plays a major role in the molecular mechanisms that govern nicotine withdrawal. Thus, elucidating how expression of the β4 gene is regulated is critical for understanding the pathophysiology of nicotine addiction. We previously identified a CA box regulatory element, (5'-CCACCCCT-3') critical for β4 promoter activity in vitro. We further demonstrated that a 2.3-kb fragment of the β4 promoter region containing the 5'-CCACCCCT-3' regulatory element in the β4 gene promoter (CA box) is capable of directing cell-type specific expression of a reporter gene to a myriad of brain regions that endogenously express the β4 gene. To test the hypothesis that the CA box is critical for β4 promoter activity in vivo, transgenic animals expressing a mutant form of the β4 promoter were generated. Reporter gene expression was not detected in any tissue or cell type at embryonic day 18.5 (ED 18.5). Similarly, we observed drastically reduced reporter gene expression at postnatal day 30 (PD30) when compared to wild type (WT) transgenic animals. Finally, we demonstrated that CA box mutation results in decreased interaction of the transcription factor Sp1 with the mutant β4 promoter. Taken together these results demonstrate that the CA box is critical for β4 promoter activity in vivo.

The nicotinic acetylcholine receptor CHRNA5/A3/B4 gene cluster: dual role in nicotine addiction and lung cancer

More than 1 billion people around the world smoke, with 10 million cigarettes sold every minute. Cigarettes contain thousands of harmful chemicals including the psychoactive compound, nicotine. Nicotine addiction is initiated by the binding of nicotine to nicotinic acetylcholine receptors, ligand-gated cation channels activated by the endogenous neurotransmitter, acetylcholine. These receptors serve as prototypes for all ligand-gated ion channels and have been extensively studied in an attempt to elucidate their role in nicotine addiction. Many of these studies have focused on heteromeric nicotinic acetylcholine receptors containing α4 and β2 subunits and homomeric nicotinic acetylcholine receptors containing the α7 subunit, two of the most abundant subtypes expressed in the brain. Recently however, a series of linkage analyses, candidate-gene analyses and genome-wide association studies have brought attention to three other members of the nicotinic acetylcholine receptor family: the α5, α3 and β4 subunits. The genes encoding these subunits lie in a genomic cluster that contains variants associated with increased risk for several diseases including nicotine dependence and lung cancer. The underlying mechanisms for these associations have not yet been elucidated but decades of research on the nicotinic receptor gene family as well as emerging data provide insight on how these receptors may function in pathological states. Here, we review this body of work, focusing on the clustered nicotinic acetylcholine receptor genes and evaluating their role in nicotine addiction and lung cancer.

ASCL1 regulates the expression of the CHRNA5/A3/B4 lung cancer susceptibility locus

Tobacco contains a variety of carcinogens as well as the addictive compound nicotine. Nicotine addiction begins with the binding of nicotine to its cognate receptor, the nicotinic acetylcholine receptor (nAChR). Genome-wide association studies have implicated the nAChR gene cluster, CHRNA5/A3/B4, in nicotine addiction and lung cancer susceptibility. To further delineate the role of this gene cluster in lung cancer, we examined the expression levels of these three genes as well as other members of the nAChR gene family in lung cancer cell lines and patient samples using quantitative reverse transcription-PCR. Overexpression of the clustered nAChR genes was observed in small-cell lung carcinoma (SCLC), an aggressive form of lung cancer highly associated with cigarette smoking. The overexpression of the genomically clustered genes in SCLC suggests their coordinate regulation. In silico analysis of the promoter regions of these genes revealed putative binding sites in all three promoters for achaete-scute complex homolog 1 (ASCL1), a transcription factor implicated in the pathogenesis of SCLC, raising the possibility that this factor may regulate the expression of the clustered nAChR genes. Consistent with this idea, knockdown of ASCL1 in SCLC, but not in non-SCLC, led to a significant decrease in expression of the alpha 3 and beta 4 genes without having an effect on any other highly expressed nAChR gene. Our data indicate a specific role for ASCL1 in regulating the expression of the CHRNA5/A3/B4 lung cancer susceptibility locus. This regulation may contribute to the predicted role that ASCL1 plays in SCLC tumorigenesis.

The armadillo repeat-containing protein, ARMCX3, physically and functionally interacts with the developmental regulatory factor Sox10

Sox10 is a member of the group E Sox transcription factor family and plays key roles in neural crest development and subsequent cellular differentiation. Sox10 binds to regulatory sequences in target genes via its conserved high mobility group domain. In most cases, Sox10 exerts its transcriptional effects in concert with other DNA-binding factors, adaptor proteins, and nuclear import proteins. These interactions can lead to synergistic gene activation and can be cell type-specific. In earlier work, we demonstrated that Sox10 transactivates the nicotinic acetylcholine receptor alpha3 and beta4 subunit genes and does so only in neuronal-like cell lines, raising the possibility that Sox10 mediates its effects via interactions with co-regulatory factors. Here we describe the identification of the armadillo repeat-containing protein, ARMCX3, as a Sox10-interacting protein. Biochemical analyses indicate that ARMCX3 is an integral membrane protein of the mitochondrial outer membrane. Others have shown that Sox10 is a nucleocytoplasmic shuttling protein. We extend this observation and demonstrate that, in the cytoplasm, Sox10 is peripherally associated with the mitochondrial outer membrane. Both Sox10 and ARMCX3 are expressed in mouse brain and spinal cord as well as several cell lines. Overexpression of ARMCX3 increased the amount of mitochondrially associated Sox10. In addition, although ARMCX3 does not possess intrinsic transcriptional activity, it does enhance transactivation of the nicotinic acetylcholine receptor alpha3 and beta4 subunit gene promoters by Sox10. These results suggest that Sox10 is a membrane-associated factor whose transcriptional function is increased by direct interactions with ARMCX3 and raise the possibility of a signal transduction cascade between the nucleus and mitochondria through Sox10/ARMCX3 interactions.

Transcription factor assembly on the nicotinic receptor beta4 subunit gene promoter

Nicotinic acetylcholine receptors are involved in a plethora of fundamental biological processes ranging from muscle contraction to formation of memories. The receptors are pentameric proteins whose subunits are encoded by distinct genes. Subunit composition of a mature nicotinic receptor is governed in part by the transcriptional regulation of each subunit gene. Here, using chromatin immunoprecipitation assays, we report the interaction of the transcription factors Sp1, Sp3, c-Jun and Sox10 with the beta4 subunit gene promoter in neuronal-like cell lines and rodent brain tissue. Our results corroborate previous in-vitro data demonstrating that these transcription factors interact with the beta4 promoter. Taken together, these data suggest that Sp1, Sp3, c-Jun and Sox10 regulate expression of the beta4 subunit gene in the mammalian brain.

Transcriptional Repression by a Conserved Intronic Sequence in the Nicotinic Receptor α3 Subunit Gene

The genes encoding the nicotinic acetylcholine receptor alpha3, alpha5, and beta4 subunits are genomically clustered. These genes are co-expressed in a variety of cells in the peripheral and central nervous systems. Their gene products assemble in a number of stoichiometries to generate several nicotinic receptor subtypes that have distinct pharmacological and physiological properties. Signaling through these receptors is critical for a variety of fundamental biological processes. Despite their importance, the transcriptional mechanisms underlying their coordinated expression remain to be completely elucidated. By using a bioinformatics approach, we identified a highly conserved intronic sequence within the fifth intron of the alpha3 subunit gene. Reporter gene analysis demonstrated that this sequence, termed "alpha3 intron 5," inhibits the transcriptional activities of the alpha3 and beta4 subunit gene promoters. This repressive activity is position- and orientation-independent. Importantly, repression occurs in a cell type-specific manner, being present in cells that do not express the receptor genes or expresses them at very low levels. Electrophoretic mobility shift assays demonstrate that nuclear proteins specifically interact with alpha3 intron 5 at two distinct sites. We propose that this intronic repressor element is important for the restricted expression patterns of the nicotinic receptor alpha3 and beta4 subunit genes.

Functional Difference of the SOX10 Mutant Proteins Responsible for the Phenotypic Variability in Auditory-Pigmentary Disorders

Waardenburg syndrome (WS) is an inherited disorder, characterized by auditory-pigmentary abnormalities. SOX10 transcription factor and endothelin receptor type B (EDNRB) are responsible for WS type 4 (WS4), which also exhibits megacolon, while microphthalmia-associated transcription factor (MITF) is responsible for WS2, which is not associated with megacolon. Here, we investigated the functions of SOX10 mutant proteins using the target promoters, EDNRB and MITF. The SOX10 mutations chosen were E189X, Q377X, and 482ins6, which are associated with WS4, and S135T that is associated with Yemenite deaf-blind hypopigmentation syndrome (YDBS), which does not manifest megacolon. These SOX10 mutant proteins showed impaired transactivation activity on the MITF promoter. In contrast, E189X and Q377X proteins, each of which lacks its C-terminal portion, activated the EDNRB promoter, whereas no activation was detected with the SOX10 proteins mutated at the DNA-binding domain, 482ins6 and S135T. However, unlike 482ins6 protein, S135T protein synergistically activated EDNRB promoter with a transcription factor Sp1, indicating that Sp1 could compensate the impaired function of a SOX10 mutant protein. We suggest that the variability in transactivation ability of SOX10 mutant proteins may account for the different phenotypes between WS4 and YDBS and that Sp1 is a potential modifier gene of WS4.

SOX10, in combination with Sp1, regulates the endothelin receptor type B gene in human melanocyte lineage cells

Waardenburg syndrome (WS) is an auditory-pigmentary disorder that exhibits varying combinations of sensorineural hearing loss and abnormal pigmentation of the hair and skin. WS type 4 (WS4), a subtype of WS, is characterized by the presence of the aganglionic megacolon and is associated with mutations in the gene encoding either endothelin 3, endothelin receptor type B (EDNRB), or Sry-box 10 (SOX10). Here, we provide evidence that SOX10 regulates the expression of EDNRB gene in human melanocyte-lineage cells, as judged by RNA interference and chromatin immunoprecipitation analyses. Human melanocytes preferentially express the EDNRB transcripts derived from the conventional EDNRB promoter. SOX10 transactivates the EDNRB promoter through the cis-acting elements, the two CA-rich sequences and the GC box. Moreover, a transcription factor Sp1 enhances the degree of the SOX10-mediated transactivation of the EDNRB promoter through these cis-acting elements. Furthermore, we have shown that the EDNRB promoter is heavily methylated in HeLa human cervical cancer cells, lacking EDNRB expression, but not in melanocytes and HMV-II melanoma cells. The expression of EDNRB became detectable in HeLa cells after treatment with a demethylating reagent, 5'-aza-2'-deoxycytidine, which was further enhanced in the transformed cells over-expressing SOX10. We therefore suggest that SOX10, alone or in combination with Sp1, regulates transcription of the EDNRB gene, thereby ensuring appropriate expression level of EDNRB in human melanocytes.

Sox10 acts as a tissue-specific transcription factor enhancing activation of the myelin basic protein gene promoter by p27Kip1 and Sp1

Myelin basic protein (MBP) is one of the major components of the myelin sheath that insulates axons. In the central nervous system, MBP is synthesized by differentiating oligodendrocytes. The expression of MBP in oligodendrocytes is regulated mainly at the transcriptional level. The Sp1 family of transcription factors has been shown to be important in the regulation of many genes. Binding of Sp1 to the GC box in the proximal MBP promoter has been shown to be indispensable for the activation of MBP gene expression. Previous results from our laboratory have shown that the increase in p27Kip1 that accompanies oligodendrocyte differentiation is paralleled by an increase in Sp1. We also have shown that the increase in MBP expression resulting from elevated p27Kip1 levels is mediated through Sp1 and that this effect occurs specifically in oligodendrocytes. In this study, we found that increased expression of p27Kip1 together with the nervous-system-specific transcription factor Sox10 can activate the MBP promoter even in nonoligodendrocyte cells. This indicates that Sox10 confers cell type specificity on the expression of MBP. Both Sp1 and Sox10 can enhance MBP promoter activity when expressed alone. Cotransfection of plasmids encoding Sp1 and Sox10 induces increased activation of the MBP promoter over expression of either transcription factor alone. This effect is not limited to oligodendrocyte cell lines, in that Sp1 and Sox10 can also synergistically activate the MBP promoter when expressed in NIH3T3 fibroblasts. Mutation of the Sp1 binding sites in the MBP promoter eliminates Sox10 stimulated activation, suggesting that the MBP promoter is activated, at least in part, through protein-protein interactions between Sp1 and Sox10.

SNCF, a SoxNeuro interacting protein, defines a novel protein family in Drosophila melanogaster

The involvement of the Sox family of transcription factors in the development of the central nervous system (CNS) appears to be conserved in invertebrates and vertebrates. In Drosophila, SoxNeuro (SoxN) was recently shown to be involved in the formation of neuroblasts [Development 129 (2002) 4193; Development 129 (2002) 4219]. Through a yeast two-hybrid assay searching for proteins interacting with SoxN, we have isolated a novel protein in Drosophila, SoxNeuro Co-Factor (SNCF). The expression of the SNCF gene was detected during early embryogenesis at the blastoderm stages, and stopped just at the beginning of gastrulation. In transfected cells, the protein localised to nuclei, and strongly accumulated in nucleoli. SNCF was able to enhance SoxN mediated transcriptional activity in transfected cells, suggesting that SNCF might act as a SoxN co-activator. Finally, data are presented showing the existence in Drosophila of several proteins with a domain of homology to SNCF, which are all expressed early in embryogenesis at the blastoderm stage.

The importance of having your SOX on: role of SOX10 in the development of neural crest-derived melanocytes and glia

SOX10 is a member of the high-mobility group-domain SOX family of transcription factors, which are ubiquitously found in the animal kingdom. Disruption of neural crest development in the Dominant megacolon (Dom) mice is associated with a Sox10 mutation. Mutations in human Sox10 gene have also been linked with the occurrence of neurocristopathies in the Waardenburg-Shah syndrome type IV (WS-IV), for which the Sox10(Dom) mice serve as a murine model. The neural crest disorders in the Sox10(Dom) mice and WS-IV patients consist of hypopigmentation, cochlear neurosensory deafness, and enteric aganglionosis. Consistent with these observations, a critical role for SOX10 in the proper differentiation of neural crest-derived melanocytes and glia has been demonstrated. Emerging data also show an important role for SOX10 in promoting the survival of neural crest precursor cells prior to lineage commitment. Several genes whose regulation is dependent on SOX10 function have been identified in the peripheral nervous system and in melanocytes, helping to begin the identification of the multiple pathways that appear to be modulated by SOX10 activity. In this review, we will discuss the biological relevance of these target genes to neural crest development and the properties of Sox10 as a transcription factor.

Activation of myelin genes during transdifferentiation from melanoma to glial cell phenotype

Induction of myelin genes occurs around birth in the last stage of Schwann cells differentiation and is reactivated in case of nerve injury. Previous studies showed that activation of the gp130 receptor system, using as ligand interleukin-6 fused to its soluble receptor (IL6RIL6), causes induction of myelin genes such as myelin basic protein (MBP) and myelin protein zero (Po) in embryonic dorsal root ganglia Schwann cells. We also reported that in murine melanoma B16/F10.9 cells, IL6RIL6 causes a shut-off of melanogenesis mediated by a down-regulation of the paired-homeodomain factor Pax3. The present work demonstrates that these IL6RIL6-treated F10.9 cells undergo transdifferentiation to a myelinating glial phenotype characterized by induction of the transcriptional activities of both Po and MBP promoters and accumulation of myelin gene products. For both Po and MBP promoters, a repression by Pax3 and stimulation by Sox10 can be demonstrated. Because after IL6RIL6-treatment, Pax3 disappears from the F10.9 cells (as it does in mature myelinating Schwann cells) whereas the level of Sox10 rather increases, we modulated the relative level of these factors and show their involvement in the induction of myelin gene expression by IL6RIL6. In addition, however, we show that a C/G-rich CACC box in the Po promoter is required for activation by IL6RIL6, as well as by ectopic Sox10, and identify a Kruppel-type zinc finger factor acting through this CACC box, which stimulates Po promoter activity.

Sp1 and Sp3 transcription factors synergistically regulate HGF receptor gene expression in kidney

We investigated the expression pattern and underlying mechanism that controls hepatocyte growth factor (HGF) receptor (c-met) expression in normal kidney and a variety of kidney cells. Immunohistochemical staining showed widespread expression of c-met in mouse kidney, a pattern closely correlated with renal expression of Sp1 and Sp3 transcription factors. In vitro, all types of kidney cells tested expressed different levels of c-met, which was tightly proportional to the cellular abundances of Sp1 and Sp3. Both Sp1 and Sp3 bound to the multiple GC boxes in the promoter region of the c-met gene. Coimmunoprecipitation suggested a physical interaction between Sp1 and Sp3. Functionally, Sp1 markedly stimulated c-met promoter activity. Although Sp3 only weakly activated the c-met promoter, its combination with Sp1 synergistically stimulated c-met transcription. Conversely, deprivation of Sp proteins by transfection of decoy Sp1 oligonucleotide or blockade of Sp1 binding with mithramycin A inhibited c-met expression. The c-met receptor in all types of kidney cells was functional and induced protein kinase B/Akt phosphorylation in a distinctly dynamic pattern after HGF stimulation. These results indicate that members of the Sp family of transcription factors play an important role in regulating constitutive expression of the c-met gene in all types of renal cells. Our findings suggest that HGF may have a broader spectrum of target cells and possess wider implications in kidney structure and function than originally thought.

Matching SOX: partner proteins and co-factors of the SOX family of transcriptional regulators

SOX transcription factors perform a remarkable variety of important roles in vertebrate development, either activating or repressing specific target genes through interaction with different partner proteins. Surprisingly, these interactions are often mediated by the conserved, DNA-binding HMG domain, raising questions as to how each factor's specificity is generated. We propose a model whereby non-HMG domains may influence partner protein selection and/or binding stability.

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.

Floppy SOX: mutual induced fit in hmg (high-mobility group) box-DNA recognition

The high-mobility group (HMG) box defines a DNA-bending motif of broad interest in relation to human development and disease. Major and minor wings of an L-shaped structure provide a template for DNA bending. As in the TATA-binding protein and a diverse family of factors, insertion of one or more side chains between base pairs induces a DNA kink. The HMG box binds in the DNA minor groove and may be specific for DNA sequence or distorted DNA architecture. Whereas the angular structures of non-sequence-specific domains are well ordered, free SRY and related autosomal SOX domains are in part disordered. Observations suggesting that the minor wing lacks a fixed tertiary structure motivate the hypothesis that DNA bending and stabilization of protein structure define a coupled process. We further propose that mutual induced fit in SOX-DNA recognition underlies the sequence dependence of DNA bending and enables the induction of promoter-specific architectures.