Isolation of two cDNAs encoding zinc finger proteins which bind to the alpha 1-antitrypsin promoter and to the major histocompatibility complex class I enhancer

Genome-wide repression of NF-κB target genes by transcription factor MIBP1 and its modulation by O-linked β-N-acetylglucosamine (O-GlcNAc) transferase

The transcription factor c-MYC intron binding protein 1 (MIBP1) binds to various genomic regulatory regions, including intron 1 of c-MYC. This factor is highly expressed in postmitotic neurons in the fetal brain and may be involved in various biological steps, such as neurological and immunological processes. In this study, we globally characterized the transcriptional targets of MIBP1 and proteins that interact with MIBP1. Microarray hybridization followed by gene set enrichment analysis revealed that genes involved in the pathways downstream of MYC, NF-κB, and TGF-β were down-regulated when HEK293 cells stably overexpressed MIBP1. In silico transcription factor binding site analysis of the promoter regions of these down-regulated genes showed that the NF-κB binding site was the most overrepresented. The up-regulation of genes known to be in the NF-κB pathway after the knockdown of endogenous MIBP1 in HT1080 cells supports the view that MIBP1 is a down-regulator of the NF-κB pathway. We also confirmed the binding of the MIBP1 to the NF-κB site. By immunoprecipitation and mass spectrometry, we detected O-linked β-N-acetylglucosamine (O-GlcNAc) transferase as a prominent binding partner of MIBP1. Analyses using deletion mutants revealed that a 154-amino acid region of MIBP1 was necessary for its O-GlcNAc transferase binding and O-GlcNAcylation. A luciferase reporter assay showed that NF-κB-responsive expression was repressed by MIBP1, and stronger repression by MIBP1 lacking the 154-amino acid region was observed. Our results indicate that the primary effect of MIBP1 expression is the down-regulation of the NF-κB pathway and that this effect is attenuated by O-GlcNAc signaling.

Mint Represses Transactivation of the Type II Collagen Gene Enhancer through Interaction with αA-crystallin-binding Protein 1

Collagen type II is an extracellular matrix protein important for cartilage and bone formation, and its expression is controlled by multiple cis- and trans-acting elements, including the zinc finger transcription factor alpha A-crystallin-binding protein 1 (CRYBP1). Here we show that MSX2-interacting nuclear target protein (MINT), a conserved transcriptional repressor, associates with CRYBP1 and negatively regulates the transactivation of the collagen type II gene (Col2a1) enhancer. We identified CRYBP1 as a binding partner of MINT by screening a mouse embryonic cDNA library using the yeast two-hybrid system. We demonstrated that the C terminus of MINT interacts with the C terminus of CRYBP1 using the mammalian cell two-hybrid assay, glutathione S-transferase pull-down, and co-immunoprecipitation analyses. Furthermore, MINT and CRYBP1 form a complex on the Col2a1 enhancer, as shown by chromatin immunoprecipitation and gel shift assays. In the presence of CRYBP1, overexpression of MINT or its C-terminal fragment in cells repressed a reporter construct driven by the Col2a1 enhancer elements. This transcription repression is dependent on histone deacetylase, the main co-repressor recruited by MINT. The present study shows that MINT is involved in CRYBP1-mediated Col2a1 gene repression and may play a role in regulation of cartilage development.

Frequent down-regulation of HIVEP2 in human breast cancer

The HIVEP2 gene, located on 6q23-q24, belongs to a family of genes that encodes large zinc fingers containing transcription factor proteins. Although this gene has been implicated in the regulation of immune responses and cellular proliferation, its functions are largely unknown. In the present study, we investigated HIVEP2 gene abnormalities in microdissected breast cancer tissue. For real-time quantitational RT-PCR analysis of paired normal and tumor tissues, mRNA levels were down-regulated to a maximum of 96%. The overall median expression level in breast cancer (33 cases) was significantly lower than that in normal breast tissue (normalized median value of 4.49 versus 17.68; p < 0.0001). Through full-length 5'-RACE (rapid amplification of cDNA ends) analysis, we identified multiple exons in the 5'-untranslated regions with multiple transcriptional start sites, four of which were located in a large CpG island. No tissue- or cancer-specific usage patterns for the transcription start sites were identified by multiplex RT-PCR analysis. Only faint methylation was detected in the 5' region of the island in normal cells and breast cancer tissue, indicating physiological, aging and no tumor-specific methylation. Mutation screening showed only germline polymorphisms. Thus, down-regulation of the HIVEP2 genes frequently occurs and may be one of the genetic events responsible for breast cancer, and their transcription may be regulated by complex mechanisms involving interactions with other factors and/or by other genetic/epigenetic mechanisms.

Cloning and initial characterization of an alternatively spliced transcript encoded by the bovine herpes virus 1 latency-related gene

Bovine herpesvirus 1 (BHV-1) establishes latency in trigeminal ganglionic sensory neurons of infected cattle. The latency-related (LR) RNA is the only abundantly expressed viral transcript in sensory neurons of latently infected calves. Wild-type expression of LR gene products is required for the latency-reactivation cycle in calves. LR RNA is alternatively spliced in trigeminal ganglia (TG) after infection of calves, suggesting that these alternatively spliced transcripts encode novel factors that regulate specific steps during latency. To begin testing whether these alternatively spliced transcripts have novel functions, the authors cloned a full-length cDNA identified in TG of calves at 7 days post infection (dpi) and compared the functions of this cDNA to the intact LR gene. As a result of splicing, the 7 dpi cDNA contains a novel open reading (ORF) comprised of OFR-2 fused to ORF-1. Overexpression of the 7 dpi cDNA inhibited the BHV-1 immediate-early transcription unit 1 (IEtu1) promoter and the herpes simplex virus type 1 ICP0 promoter. Conversely, the 7 dpi cDNA stimulated the LR promoter in transiently transfected cells. A plasmid containing the LR gene had little effect on IEtu1 or LR promoter activity, indicating that the 7 dpi cDNA has novel functions.

ZAS: C2H2 zinc finger proteins involved in growth and development

A ZAS gene encodes a large protein with two separate C2H2 zinc finger pairs that independently bind to specific DNA sequences, including the kappaB motif. Three paralogous mammalian genes, ZAS1, ZAS2, and ZAS3, and a related Drosophila gene, Schnurri, have been cloned and characterized. The ZAS genes encode transcriptional proteins that activate or repress the transcription of a variety of genes involved in growth, development, and metastasis. In addition, ZAS3 associates with a TNF receptor-associated factor to inhibit NF-kappaB- and JNK/ SAPK-mediated signaling of TNF-alpha. Genetic experiments show that ZAS3 deficiency leads to proliferation of cells and tumor formation in mice. The data suggest that ZAS3 is important in controlling cell growth, apoptosis, and inflammation. The potent vasoactive hormone endothelin and transcription factor AP2 gene families also each consist of three members. The ZAS, endothelin, and transcription factor AP2 genes form several linkage groups. Knowledge of the chromosomal locations of these genes provides valuable clues to the evolution of the vertebrate genome.

Structure of the human zinc finger protein HIVEP3: molecular cloning, expression, exon-intron structure, and comparison with paralogous genes HIVEP1 and HIVEP2

Here we report the cloning and characterization of HIVEP3, the newest member in the human immunodeficiency virus type 1 enhancer-binding protein family that encodes large zinc finger proteins and regulates transcription via the kappaB enhancer motif. The largest open reading frame of HIVEP3 contains 2406 aa. and is approximately 80% identical to the mouse counterpart. The HIVEP3 gene is located in the chromosomal region 1p34 and is at least 300 kb with 10 exons. RNA studies show that multiple HIVEP3 transcripts are differentially expressed and regulated. Additionally, transcription termination occurs in the ultimate exon, exon 10, or in exon 6. Therefore, HIVEP3 may produce protein isoforms that contain or exclude the carboxyl DNA binding domain and the leucine zipper by alternative RNA splicing and differential polyadenylation. Sequence homologous to HIVEP3 exon 6 is not found in mouse nor are the paralogous genes HIVEP1 and HIVEP2. Zoo-blot analysis suggests that sequences homologous to the human exon 6 are present only in primates and cow. Therefore, a foreign DNA harboring a termination exon likely was inserted into the HIVEP3 locus relatively recently in evolution, resulting in the acquisition of novel gene regulatory mechanisms as well as the generation of structural and functional diversity.

Schnurri mediates Dpp-dependent repression of brinker transcription

Signalling by Decapentaplegic (Dpp), a member of the TGFbeta superfamily of signalling molecules, controls many aspects of Drosophila development by activating and repressing target genes. Several essential components of the Dpp signalling pathway have been identified, including the Dpp receptors Punt and Thick veins (Tkv) as well as the cytoplasmic mediators Mad and Medea. For target genes to be activated, Dpp signalling must suppress transcription of a repressor encoded by the brinker (brk) gene. Here we show that Schnurri (Shn), a large zinc-finger protein, is essential for Dpp-mediated repression of brk transcription; in contrast, Shn is not required for target-gene activation. Thus, the Dpp signalling pathway bifurcates, downstream of the signal-mediating SMAD proteins, into a Shn-dependent pathway leading to brk repression and a Shn-independent pathway leading to gene activation. The existence of several Shn-like proteins in vertebrates and the observation that Brk functions in BMP signalling in Xenopus indicates that a similar regulatory cascade may be conserved in higher organisms.

A zinc finger transcription factor, alphaA-crystallin binding protein 1, is a negative regulator of the chondrocyte-specific enhancer of the alpha1(II) collagen gene

Transcription of the type II collagen gene (Col2a1) is regulated by multiple cis-acting sites. The enhancer element, which is located in the first intron, is necessary for high-level and cartilage-specific expression of Col2a1. A mouse limb bud cDNA expression library was screened by the Saccharomyces cerevisiae one-hybrid screening method to identify protein factors bound to the enhancer. A zinc finger protein, alphaA-crystallin binding protein 1 (CRYBP1), which had been reported to bind to the mouse alphaA-crystallin gene promoter, was isolated. We herein demonstrate that CRYBP1 is involved in the negative regulation of Col2a1 enhancer activity. CRYBP1 mRNA expression was downregulated during chondrocyte differentiation in vitro. In situ hybridization analysis of developing mouse cartilage showed that CRYBP1 mRNA was also downregulated during mesenchymal condensation and that CRYBP1 mRNA was highly expressed by hypertrophic chondrocytes, but at very low levels by resting and proliferating chondrocytes. Expression of recombinant CRYBP1 in a transfected rat chondrosarcoma cell line inhibited Col2a1 enhancer activity. Electrophoretic mobility shift assays showed that CRYBP1 bound a specific sequence within the Col2a1 enhancer and inhibited the binding of Sox9, an activator for Col2a1, to the enhancer. Cotransfection of CRYBP1 with Sox9 into BALB/c 3T3 cells inhibited activation of the Col2a1 enhancer by Sox9. These results suggest a novel mechanism that negatively regulates cartilage-specific expression of Col2a1.

Schnurri interacts with Mad in a Dpp-dependent manner

BACKGROUND

Decapentaplegic (Dpp) is a member of the transforming growth factor-beta superfamily. Dpp governs various developmental processes in Drosophila through the transcriptional regulation of a variety of genes. Signals of Dpp are transmitted from the cell membrane to the nucleus by Medea and Mad, both belonging to the Smad protein family. Mad was shown to bind to the Dpp-responsive element in genes such as vestigial, labial, and Ultrabithorax. The DNA binding affinity of Smad proteins is relatively low, and requires other nuclear factor(s) to form stable DNA binding complexes. schnurri (shn) was identified as a candidate gene acting downstream of Dpp receptors, but its relevance to Mad has remained unknown.

RESULTS

We characterized the biochemical functions of Shn. Shn forms homo-oligomers. Shn is localized in the nucleus, and is likely to have multiple nuclear localizing signals. Finally, we found that Shn interacts with Mad in a Dpp-dependent manner.

CONCLUSIONS

The present results argue that Shn may act as a nuclear component of the Dpp signalling pathway through direct interaction with Mad.

Activation of somatostatin receptor II expression by transcription factors MIBP1 and SEF-2 in the murine brain

Somatostatin receptor type II expression in the mammalian brain displays a spatially and temporally very restricted pattern. In an investigation of the molecular mechanisms controlling these patterns, we have recently shown that binding of the transcription factor SEF-2 to a novel initiator element in the SSTR-2 promoter is essential for SSTR-2 gene expression. Further characterization of the promoter identified a species-conserved TC-rich enhancer element. By screening a mouse brain cDNA expression library, we cloned a cDNA encoding the transcription factor MIBP1. MIBP1 interacts specifically with both the TC box in the SSTR-2 promoter and with the SEF-2 initiator-binding protein to enhance transcription from the basal SSTR-2 promoter. We then investigated SSTR-2, SEF-2, and MIBP1 mRNA expression patterns in the developing and adult murine brain by Northern blotting and in situ hybridization. While SEF-2 is widely expressed in many neuronal and nonneuronal tissues, MIBP1 expression overlapped precisely with expression of SSTR-2 in the frontal cortex and hippocampus. In summary, our data for the first time define a regulatory role for the transcription factor MIBP1 in mediating spatially and temporally regulated SSTR-2 expression in the brain.

A Drosophila protein related to the human zinc finger transcription factor PRDII/MBPI/HIV-EP1 is required for dpp signaling

Little is known about the signal transduction pathways by which cells respond to mammalian TGF-beta s or to decapentaplegic (dpp), a Drosophila TGF-beta-related factor. Here we describe the genetic and molecular characterization of Drosophila schnurri (shn), a putative transcription factor implicated in dpp signaling. The shn protein has eight zinc fingers and is related to a human transcription factor, PRDII/MBPI/HIV-EP1, that binds to nuclear factor-kappa B-binding sites and activates transcription from the HIV long terminal repeat (LTR). shn mRNA is expressed in a dynamic pattern in the embryo that includes most of the known target tissues of dpp, including the dorsal blastoderm, the mesodermal germlayer and parasegments 4 and 7 of the midgut. Mutations in shn affect several developmental processes regulated by dpp including induction of visceral mesoderm cell fate, dorsal/ventral patterning of the lateral ectoderm and wing vein formation. Absence of shn function blocks the expanded expression of the homeodomain protein bagpipe in the embryonic mesoderm caused by ectopic dpp expression, illustrating a requirement for shn function downstream of dpp action. We conclude that shn function is critical for cells to respond properly to dpp and propose that shn protein is the first identified downstream component of the signal transduction pathway used by dpp and its receptors.

Murine transcription factor alpha A-crystallin binding protein I. Complete sequence, gene structure, expression, and functional inhibition via antisense RNA

alpha A-crystallin binding protein I (alpha A-CRYBP1) is a ubiquitously expressed DNA binding protein that was previously identified by its ability to interact with a functionally important sequence in the mouse alpha A-crystallin gene promoter. Here, we have cloned a single copy gene with 10 exons spanning greater than 70 kb of genomic DNA that encodes alpha A-CRYBP1. The mouse alpha A-CRYBP1 gene specifies a 2,688-amino acid protein with 72% amino acid identity to its human homologue, PRDII-BF1. Both the human and the mouse proteins contain two sets of consensus C2H2 zinc fingers at each end as well a central nonconsensus zinc finger. The alpha A-CRYBP1 gene produces a 9.5-kb transcript in 11 different tissues as well as a testis-specific, 7.7-kb transcript. alpha A-CRYBP1 cDNA clones were isolated from adult mouse brain and testis as well as from cell lines derived from mouse lens (alpha TN4-1) and muscle (C2C12). A single clone isolated from the muscle C2C12 library contains an additional exon near the 5'-end that would prevent production of a functional protein if the normal translation start site were utilized; however, there is another potential initiation codon located downstream that is in frame with the rest of the coding region. In addition, we identified multiple cDNAs from the testis in which the final intron is still present. Finally, we used an antisense expression construct derived from an alpha A-CRYBP1 cDNA clone to provide the first functional evidence that alpha A-CRYBP1 regulates gene expression. When introduced into the alpha TN4-1 mouse lens cell line, the antisense construct significantly inhibited expression from a heterologous promoter that utilized the alpha A-CRYBP1 binding site as an enhancer.

Cloning and characterization of a c-myc intron binding protein (MIBP1)

The cDNA for a c-myc intron 1 binding protein 1 (MIBP1) in the rat was isolated from lambda gt11 and lambda ZAPII cDNA libraries. Sequencing of the cDNA clones revealed a long ORF which encoded a putative protein of 2437 amino acid residues. This protein has two widely separated zinc finger regions, each of which carries C2H2 motifs. When expressed in E. coli as a fusion protein, part of the MIBP1 showed sequence-specific binding to the target sequence, i.e., a 9-bp sequence in the rat c-myc intron 1. MIBP1 is most likely the rat counterpart of human MHC binding protein-2 (MBP-2/HIV-EP2), based on the 86% similarity in nucleotide sequence and 93% similarity in amno acid sequence. Northern blotting revealed a high level of MIBP1 mRNA in the brain.

Stereochemical basis of DNA recognition by Zn fingers

DNA-recognition rules for Zn fingers are discussed in terms of crystal structures. The rules can explain the DNA-binding characteristics of a number of Zn finger proteins for which there are no crystal structures. The rules have two parts: chemical rules, which list the possible pairings between the 4 DNA bases and the 20 amino acid residues, and stereochemical rules, which describe the specific base positions contacted by several amino acid positions in the Zn finger. It is discussed that to maintain the correct binding geometry, in which the N-terminus of the recognition helix is closer to the DNA than the C-terminus, the residues facing the DNA on the helix must be larger near the C-terminus, and that two different types of fingers (A and B) bind to DNA in distinctly different ways and cover different numbers of base pairs.

Putative nuclear localization signals (NLS) in protein transcription factors

We have recognized about ten distinct forms of strongly basic hexapeptides, containing at least four arginines and lysines, characteristic of nuclear proteins among all eukaryotic species, including yeast, plants, flies and mammals. These basic hexapeptides are considered to be different versions of a core nuclear localization signal, NLS. Core NLSs are present in nearly all nuclear proteins and absent from nearly all "nonassociated" cytoplasmic proteins that have been investigated. We suggest that the few (approximately 10%) protein factors lacking a typical NLS core peptide may enter the nucleus via their strong crosscomplexation with their protein factor partners that possess a core NLS. Those cytoplasmic proteins found to possess a NLS-like peptide are either tightly associated with cell membrane proteins or are integral components of large cytoplasmic protein complexes. On the other hand, some versions of core NLSs are found in many cell membrane proteins and secreted proteins. It is hypothesized that in these cases the N-terminal hydrophobic signal peptide of extracellular proteins and the internal hydrophobic domains of transmembrane proteins are stronger determinants for their subcellular localization. The position of core NLSs among homologous nuclear proteins may or may not be conserved; however, if lost from an homologous site it appears elsewhere in the protein. This search provides a set of rules to our understanding of the nature of core nuclear localization signals: (1) Core NLS are proposed to consist most frequently of an hexapeptide with 4 arginines and lysines; (2) aspartic and glutamic acid residues as well as bulky amino acids (F, Y, W) need not to be present in this hexapeptide; (3) acidic residues and proline or glycine that break the alpha-helix are frequently in the flanking region of this hexapeptide stretch; (4) hydrophobic residues ought not to be present in the core NLS flanking region allowing for the NLS to be exposed on the protein. In this study we attempt to classify putative core NLS from a wealth of nuclear protein transcription factors from diverse species into several categories, and we propose additional core NLS structures yet to be experimentally verified.

Molecular cloning of a zinc finger protein which binds to the heptamer of the signal sequence for V(D)J recombination

The somatic V(D)J recombination for the assembly of the Ig and TCR genes is mediated by the recombination signal sequences (Rss) and the V(D)J recombinase. A cDNA clone was isolated from a lambda gt11 expression library made from mouse thymocyte poly(A)+ RNA, using the Rss as a ligand. The deduced amino acid sequence of the putative protein, designated Recognition component (Rc), reveals a pair of Cys2-His2 zinc fingers followed by a Glu- and Asp-rich acidic domain. In addition, there are five copies of the Ser/Thr-Pro-X-Arg/Lys sequence, which are putative DNA binding units. The zinc finger-acidic domain structures present in Rc are also found in several enhancer binding proteins, such as those for the kappa B motif of the Ig kappa light chain enhancer or related sequences. Bacterial fusion proteins for Rc bind preferentially to the Rss heptamer and to the kappa B motif. The dual affinities of Rc for the Rss heptamer and the kappa B motif suggest a possible link between Ig transcription and somatic recombination. The formation of multiple 'gel-shifted' DNA-protein complexes for Rc and its DNA ligand suggests that these complexes tend to multimerize.

Binding of tissue-specific forms of alpha A-CRYBP1 to their regulatory sequence in the mouse alpha A-crystallin-encoding gene: double-label immunoblotting of UV-crosslinked complexes

The alpha A-CRYBP1 regulatory sequence (alpha A-CRYBP1RS), at nucleotides -66 to -57 of the mouse alpha A-crystallin-encoding gene (alpha A-CRY) promoter, is an important control element involved in the regulation of mouse alpha A-CRY expression. The gene encoding a protein (alpha A-CRYBP1) that specifically binds to the alpha A-CRYBP1RS sequence has been cloned from a cultured mouse lens cell line. In the present study, we have used an antibody (specific to the alpha A-CRYBP1 protein and made against a synthetic peptide) to directly identify UV-crosslinked protein-DNA complexes via a double-label immunoblotting technique. Multiple alpha A-CRYB1 antigenically related proteins interacted with alpha A-CRYBP1RS in nuclear extracts from both a cloned mouse lens cell line (alpha TN4-1) that expresses alpha A-CRY and a mouse fibroblast line (L929) that does not express the gene. Two sizes (50 kDa and 90 kDa) of proteins reacting with the alpha A-CRYBP1-specific Ab were detected in both cell lines and, in addition, a > 200-kDa protein reacting with the Ab was unique to the fibroblast line. Thus, alpha A-CRYBP1 antigenically related proteins interact with alpha A-CRYBP1RS regardless of alpha A-CRY expression. Moreover, differential processing of the alpha A-CRYBP1 protein and/or alternative splicing of the alpha A-CRY transcript may affect expression of alpha A-CRY.

A mRNA localized to the vegetal cortex of Xenopus oocytes encodes a protein with a nanos-like zinc finger domain

mRNAs concentrated in specific regions of the oocyte have been found to encode determinants that specify cell fate. We show that an intermediate filament fraction isolated from Xenopus stage VI oocytes specifically contains, in addition to Vg1 RNA, a new localized mRNA, Xcat-2. Like Vg1, Xcat-2 is found in the vegetal cortical region, is inherited by the vegetal blasomeres during development, and is degraded very early in development. Sequence analysis suggests that Xcat-2 encodes a protein that belongs to the CCHC RNA-binding family of zinc finger proteins. Interestingly, the closest known relative to Xcat-2 in this family is nanos, an RNA localized to the posterior pole of the Drosophila oocyte whose protein product suppresses the translation of the transcription factor hunchback. The localized and maternally restricted expression of Xcat-2 RNA suggests a role for its protein in setting up regional differences in gene expression that occur early in development.

Structure and expression of major histocompatibility complex-binding protein 2, a 275-kDa zinc finger protein that binds to an enhancer of major histocompatibility complex class I genes

We have isolated a cDNA encoding a transcription factor that binds to the enhancer of major histocompatibility complex (MHC) class I genes. MHC-binding protein 2 (MBP-2) is a 275-kDa protein, containing two sets of widely separated zinc fingers and a stretch of highly acidic amino acids, a putative transactivation domain. The two zinc finger regions, when expressed individually as bacterial fusion proteins, bind with highest affinity to the MHC class I gene enhancer. Several proteins found in mammalian nuclear extracts bind the MHC class I enhancer in an electrophoresis mobility shift assay. Only one of these, a ubiquitously expressed factor, forming a slow-migrating retarded complex, can be supershifted by a MBP-2 antiserum. The same antiserum also precipitates a protein of greater than 250 kDa from COS cells transfected with a MBP-2 expression vector. Our data indicate that MBP-2 is a transcription factor involved in the regulation of MHC class I gene expression.

DNA-binding properties of the E1A-associated 300-kilodalton protein

One of the major E1A-associated cellular proteins is a 300-kDa product (p300) that binds to the N-terminal region of the E1A products. The p300 binding site is distinct from sequences involved in binding the retinoblastoma product and other E1A-associated cellular products such as p60-cyclin A and p107. p300 binding to E1A is linked genetically to the enhancer repression function of E1A and the other E1A-mediated gene-regulating functions as well as to the transforming functions of E1A. However, the biochemical properties of p300 have not yet been characterized. We report here that p300 has an intrinsic DNA-binding activity and shows a preferential affinity for specific DNA sequences. The sequences selectively bound by p300 are related to those of a series of enhancer elements that are recognized by NF-kappa B. The direct physical interaction of p300 with enhancer elements provides a biochemical basis for the genetic evidence linking the E1A-mediated enhancer repression function with the p300-binding activity of E1A.

DNA-binding properties of the E1A-associated 300-kilodalton protein

One of the major E1A-associated cellular proteins is a 300-kDa product (p300) that binds to the N-terminal region of the E1A products. The p300 binding site is distinct from sequences involved in binding the retinoblastoma product and other E1A-associated cellular products such as p60-cyclin A and p107. p300 binding to E1A is linked genetically to the enhancer repression function of E1A and the other E1A-mediated gene-regulating functions as well as to the transforming functions of E1A. However, the biochemical properties of p300 have not yet been characterized. We report here that p300 has an intrinsic DNA-binding activity and shows a preferential affinity for specific DNA sequences. The sequences selectively bound by p300 are related to those of a series of enhancer elements that are recognized by NF-kappa B. The direct physical interaction of p300 with enhancer elements provides a biochemical basis for the genetic evidence linking the E1A-mediated enhancer repression function with the p300-binding activity of E1A.

A deletion polymorphism in the human alpha-2-macroglobulin (A2M) gene

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