Reversible silencing of enhancers by sequences derived from the human IFN-alpha promoter

Polymorphisms of the human IL-1 receptor antagonist gene and forearm bone mineral density in postmenopausal women

CONTEXT

Studies on the human interleukin 1 receptor antagonist (IL-1RA) gene polymorphism have provided conflicting data regarding the bone mass and quality.

AIM AND DESIGN

The objective of this case-control study was to investigate the association between the forearm bone mineral density (BMD) and the IL1RA gene polymorphisms.

MATERIALS AND METHODS

A total of 400 postmenopausal Bulgarian women participated in this study. BMD was measured at the forearm by X-ray absorptiometry on a DTX-100 device (Osteometer Meditech, USA). A PCR product was isolated. The alleles were scored according to their length: A1 - 410 bp - 4 repeats; A2 - 240 bp - 2 repeats; A3 - 500 bp - 5 repeats; A4 - 325 bp - 3 repeats; A5 - 595 bp - 6 repeats. All analyses were evaluated for statistical significance (χ(2)-test and T-test).

RESULTS

Four alleles were observed - A1, A2, A3, and A4. The A1A1 genotype was more common in cases with low BMD than in controls with normal BMD (95% vs. 90%, χ(2)P < 0.01). The A2A2 genotype was equally distributed among cases and controls (both 5%). The other two genotypes (A3A3 and A4A4) as well as A1A3 were present only in controls with normal BMD. The A2A2 genotype was associated with higher BMD and the A1A1 - with lower BMD at both forearm sites. The odds ratio for low BMD in the presence of the A1A1 genotype was 2.11. The etiological factor reflecting the association between the polymorphism and the disease was 0.50. In our study sample the IL1RA genetic polymorphisms were associated with the forearm BMD.

CONCLUSION

This genetic polymorphism may become a useful genetic marker for the study of osteoporosis.

An age-specific 35-kDa phosphoprotein binds to a repressor element in the ovalbumin gene promoter in the avian species Japanese quail

The ovalbumin (Ov) gene is expressed in the tubular gland cells of the avian oviduct in a specific manner under the control of developmental, tissue-specific, and hormonal cues. The expression is controlled by an array of positive and negative cis-acting elements present up to 1 kb upstream of its transcription start site. Our findings presented in this communication indicate that a well-characterized repressor element may be involved in active repression of the gene during aging. At least two proteins bind to the 25-bp sequence used in the present study encompassing the COUP adjacent repressor (CAR) element. The binding of one of the trans-acting factor that interacts with the repressor element increases during aging. This is accompanied by a decrease in transcription of the gene. The binding of the factor-to-repressor element decreases when expression of the Ov gene is induced by steroid administration. The factor has an approximate molecular weight of 35 kDa and is a phosphoprotein. It loses its ability to bind to DNA upon dephosphorylation. This makes it a potential target of various kinases/phosphatases that relay the various developmental, tissue-specific, and hormonal cues. The other trans-acting factor is a single-strand specific protein that interacts with the repressor element in an age-independent manner. These two proteins acting in conjunction may be involved in the repression of the Ov gene in old female birds where the lower circulating level of steroid hormones may be acting as an age-related cue.

DNA methylation induced changes in chromatin conformation of the promoter of the vitellogenin II gene of Japanese quail during aging

One approach to the understanding of the molecular basis of aging in higher organisms may be to use genes whose timing and rate of expression during the life span run parallel with specific functions that can be monitored. The genes for egg proteins, such as vitellogenin (VTG), which is expressed in the liver, and ovalbumin, lysozyme etc. that are expressed in the oviduct of birds, meet these requirements. Egg laying function is dependent on the production of these proteins, which, in turn, depends on the expression of their genes. In this communication we present the age-related studies on the VTG II gene of the bird, Japanese quail. The gene is expressed only in the liver and its expression is considerably lower in old birds that do not lay eggs. Comparison of the promoter region of the gene carrying the two important cis-acting elements, estrogen responsive element (ERE) and progesterone responsive element (PRE), shows it to be 100% homologous to the corresponding region of the chicken VTG II gene. Methylation of DNA and conformation of chromatin of this region were studied, as they are known to be important for regulation of expression of genes. Our studies show that in the liver of adult female quails which lay eggs, a -CCGG- sequence located in this region is hypomethylated, and the chromatin encompassing this region of the gene is relaxed. In the old, the -CCGG- sequence is hypermethylated and the chromatin is compact. This is correlated with a decrease in the expression of the gene and decrease in egg production. Further, electrophoretic mobility shift assay (EMSA) shows that the levels/affinity of specific trans-acting factors that bind to ERE and PRE present in the region, are not different in adult and old birds. Hence the methylation status of the -CCGG- sequence that is located in-between the ERE and the PRE may be crucial for the conformation of chromatin and availability of these two important cis-acting elements for the binding of the trans-acting factors. This, in turn, may downregulate the expression of the gene in old birds.

Expression of muscle creatine kinase gene of mice and interaction of nuclear proteins with MEF-2, E boxes and A/T-rich elements during aging

The changes in the expression of muscle creatine kinase (MCK) gene in the heart and skeletal muscle of mice during aging were studied. Its expression declines as a function of age in the heart, however, no age-related change is observed in the skeletal muscle. The cis-acting elements, MEF-2, E boxes and A/T rich elements present in the enhancer region of the mouse MCK gene are known to regulate the expression of the gene. Hence, these elements were subcloned and electrophoretic mobility shift assay was carried out to investigate the changes in the binding of the nuclear trans-acting protein factors of the heart with these elements as a function of age. These factors showed specificity for the respective cis-acting elements. Furthermore, the binding of these factors was found to decrease during aging which may contribute to the age-related decline in the expression of the MCK gene and activity of the heart.

Effects of steroid hormones on age-related expression and modulation of the lysozyme gene of the oviduct of Japanese quail

The expression of lysozyme gene in the oviduct of Japanese quail is age-dependent. Here we show that the expression of the gene is altered by three steroid hormones: 17beta-estradiol (E), progesterone (P) and glucocorticoid (dexamethasone, G), and their combinations E+P, E+G and P+G. We also show that the levels/affinities of transacting factors that bind to specific cis-acting elements in the promoter region of the gene change with age and after steroid administration. These factors are sequence-specific, age and steroid-dependent. It is proposed that administration of appropriate doses of steroid hormones after adulthood may extend the reproductive function and egg laying period in birds.

Arg3.1/Arc mRNA induction by Ca2+ and cAMP requires protein kinase A and mitogen-activated protein kinase/extracellular regulated kinase activation

Long-term potentiation (LTP) is a cellular model for persistent synaptic plasticity in the mammalian brain. Like several forms of memory, long-lasting LTP requires cAMP-mediated activation of protein kinase A (PKA) and is dependent on gene transcription. Consequently, activity-dependent genes such as c-fos that contain cAMP response elements (CREs) in their 5' regulatory region have been studied intensely. More recently, arg3.1/arc became of interest, because after synaptic stimulation, arg3.1/arc mRNA is rapidly induced and distributed to dendritic processes and may be locally translated there to facilitate synapse-specific modifications. However, to date nothing is known about the signaling mechanisms involved in the induction of this gene. Here we report that arg3.1/arc is robustly induced with LTP stimulation even at intensities that are not sufficient to activate c-fos expression. Unlike c-fos, the 5' regulatory region of arg3.1/arc does not contain a CRE consensus sequence and arg3.1/arc is unresponsive to cAMP in NIH3T3 and Neuro2a cells. However, in PC12 cells and primary cultures of hippocampal neurons, arg3.1/arc can be induced by cAMP and calcium. This induction requires the activity of PKA and mitogen-activated protein kinase, suggesting a neuron-specific pathway for the activation of arg3.1/arc expression.

Characterization of a novel negative regulatory element in the human interleukin 4 promoter

Interleukin 4 (IL-4) is a multifunctional cytokine that plays an important role in hematopoiesis, tumor cell growth, and cellular immune responses. Expression of the IL-4 gene is tightly controlled at the level of gene transcription, and many positive regulatory cis-elements have been identified in the proximal IL-4 promoter region. Relatively little is known about factors that downregulate IL-4 transcription. We performed a detailed deletional analysis of the proximal human IL-4 promoter and studied reporter gene activity in transiently transfected Jurkat T lymphoblasts. In this report, we characterize a novel negative regulatory element (termed P2 NRE) that is adjacent to a binding site for nuclear factor of activated T cells. Mutation of P2 NRE significantly enhanced the activity of a 175 base pair IL-4 promoter construct in transiently transfected Jurkat T lymphoblasts. Using nuclear extracts from Jurkat cells, we identify a candidate factor (termed Rep-1) that binds uniquely to the P2 NRE in DNA-binding assays. Rep-1 is not related to other factors previously shown to interact with the IL-4 promoter, and by UV cross-linking and SDS-PAGE analysis, we found that it migrates with a molecular mass of approximately 150 kDa. Characterizing the molecular mechanisms responsible for downregulating the IL-4 promoter should enhance our understanding of IL-4-gene dysregulation in disease states.

Trans-acting factors that interact with the proximal promoter sequences of ovalbumin gene are tissue-specific and age-related

Aging or deterioration of functions of various organs occurs after adulthood due to alterations in the expression of genes that maintain adulthood functions. Molecular changes that occur in regulation of genes in higher organisms after adulthood can be understood by using genes whose timing and rate of expression run parallel with specific functions during the life span. One such function is egg formation in birds which is dependent on the expression of egg protein genes, ovalbumin, lysozyme, vitellogenin, etc. Trans-acting factors are known to play a pivotal role in the regulation of transcription of genes. We show here a decrease in the level/binding of nuclear trans-acting factors with specific cis-acting elements of the promoter of the ovalbumin gene of oviduct of old Japanese quail. This parallels the decrease in the expression of the ovalbumin gene in the oviduct after adulthood. These factors are tissue-specific and bind in a cooperative and sequential manner to the ovalbumin gene promoter.

Regulation of a cell type-specific silencer in the human interleukin-3 gene promoter by the transcription factor YY1 and an AP2 sequence-recognizing factor

Negative regulation of cytokine gene transcription is an important mechanism in maintaining homeostasis of immune function. In this study, we characterized a silencer element in the human interleukin-3 gene promoter that is responsible for the cell-specific expression of interleukin-3. This silencer activity was proposed to be mediated by an unidentified nuclear inhibitory protein (NIP). In this study, we have identified two nuclear factors that are responsible for the silencer activity in T cells. The NIP element forms four specific DNA-protein complexes (designated as complexes A-D) with the Jurkat nuclear proteins. Complex A contains a nuclear protein that shares DNA-binding specificity with the transcription factor AP2 (designated as an AP2 sequence-recognizing factor (ASRF)). Formation of this ASRF complex is required for the NIP silencer function, as mutation of the ASRF-binding site abrogated the silencer activity. Complex B contains the nuclear factor YY1 (Yin-Yang 1), whose function is to down-regulate ASRF activity in the silencer. YY1 activity is supported by data from mutation and cotransfection analyses. Complexes C and D are formed by nonspecific binding proteins and do not express any regulatory activity in the NIP element. These data indicate that a cell type-specific silencer activity might be determined by a unique profile of ubiquitous transcription factors.

Antisense RNA: function and fate of duplex RNA in cells of higher eukaryotes

There is ample evidence that cells of higher eukaryotes express double-stranded RNA molecules (dsRNAs) either naturally or as the result of viral infection or aberrant, bidirectional transcriptional readthrough. These duplex molecules can exist in either the cytoplasmic or nuclear compartments. Cells have evolved distinct ways of responding to dsRNAs, depending on the nature and location of the duplexes. Since dsRNA molecules are not thought to exist naturally within the cytoplasm, dsRNA in this compartment is most often associated with viral infections. Cells have evolved defensive strategies against such molecules, primarily involving the interferon response pathway. Nuclear dsRNA, however, does not induce interferons and may play an important posttranscriptional regulatory role. Nuclear dsRNA appears to be the substrate for enzymes which deaminate adenosine residues to inosine residues within the polynucleotide structure, resulting in partial or full unwinding. Extensively modified RNAs are either rapidly degraded or retained within the nucleus, whereas transcripts with few modifications may be transported to the cytoplasm, where they serve to produce altered proteins. This review summarizes our current knowledge about the function and fate of dsRNA in cells of higher eukaryotes and its potential manipulation as a research and therapeutic tool.

Transcriptional repression of type I IFN genes

Transcriptional regulation is a consequence of the combination of both activation and repression for establishing specific patterns of eukaryotic gene expression. The regulation of the expression of type I interferon (IFN-A and IFN-B) multigene family is controlled primarily at the transcriptional level and has been widely studied as a model for understanding the mechanisms of stable repression, transient virus induction and postinduction repression of the genes. The positive and negative regulatory elements required for this on/off switch have been defined within a complex 5' upstream region of their transcription start site. The differential expression pattern of type I IFN genes is thought to involve both substitutions in the virus responsive element (VRE) and presence or absence of negatively acting sequences surrounding the VRE. In this review we discuss several mechanisms of negative regulation due to the existence of common or specific elements in the IFN-B and IFN-A genes and we summarize recent studies on transcriptional repressors that bind to these promoters.

Promoter structures and differential responses to viral and nonviral inducers of chicken type I interferon genes

Two serologically distinct type I interferons (IFNs), designated ChIFN1 and ChIFN2, are known in the chicken. ChIFN1 is encoded by a family of 10 or more genes, whereas ChIFN2 is encoded by a single gene. We show here that ChIFN1 and ChIFN2 transcripts are both strongly induced by Newcastle disease virus in primary chicken macrophages. By contrast, oral administration of the imidazoquinoline S-28463, which selectively induces IFN-alpha in mammals, led to a rapid accumulation of ChIFN1 (but not ChIFN2) transcripts in adult chicken spleen and thymus. The 5'-upstream region of the ChIFN2 gene contains a NF-kappaB consensus motif flanked by a sequence element that could serve as a binding site for transcription factor IRF-1, reminiscent of mammalian IFN-beta promoters, and it mediated powerful virus inducibility in a duck fibroblast cell line when cloned in front of a promoterless luciferase reporter gene. The 5'-upstream region of the cloned ChIFN1 gene contains two putative binding sites for IRF-1, but lacks NF-kappaB-binding sites, and it did not respond well to virus in transfected cells. Thus, the promoters of ChIFN1 and ChIFN2 genes not only exhibited differential responses to nonviral inducers in vivo, but also differed in structure and response to virus in transfected cells. These findings indicate that ChIFN2 represents the avian homolog of mammalian IFN-beta, whereas ChIFN1 seems to correspond to mammalian IFN-alpha.

Silencer activity in the interferon-A gene promoters

Interferon-A (IFN-A) differential gene expression is modulated by a complex interplay between cis-acting DNA elements and the corresponding specific trans-regulating factors. Substitutions in the proximal virus-responsive element of the interferon-A (IFN-A) promoters contribute to their differential gene expression. The 5' distal silencing region in the weakly virus-inducible murine IFN-A11 gene has been previously delimited. DNase I footprinting experiments and transient gene expression assays demonstrate identical silencing activity in equivalent regions of the genes for IFN-A11 and IFN-A4 promoters. A minimal 20-mer distal negative regulatory element (DNRE) in both promoters is necessary and sufficient for the silencing and a region in the highly inducible IFN-A4 promoter located between the silencer and the virus-responsive element overrides the silencer activity. Mutations in the central region of the DNRE, causing derepression, also altered the formation of one of the two major DNA-protein complexes. One of these contains a protein related to or identical to the high mobility group I(Y) proteins, while the other complex contains a major protein present in uninduced and virus-induced cells with a molecular mass of 38 kDa, which may be related to the silencer activity. Similar DNREs are present in other virus-uninducible IFN-A promoters, and these data suggest that a common silencer may mediate the transcriptional repression in different genes of this family.

Synergism between multiple virus-induced factor-binding elements involved in the differential expression of interferon A genes

Comparative transfection analysis of murine interferon A4 and interferon A11 promoter constructs transiently transfected in mouse L929 and human HeLa S3 cells infected with Newcastle disease virus showed that the second positive regulatory domain I-like domain (D motif), located between nucleotides -57 and -46 upstream of the transcription start site, contributes to the activation of virus-induced transcription of the interferon (IFN)-A4 gene promoter by cooperating with the positive regulatory domain I-like and TG-like domains previously described. Electrophoretic mobility shift assay performed with the virus-inducible fragments containing these motifs indicated that the binding activity that we have denoted as virus-induced factor (Génin, P., Bragança, J., Darracq, N., Doly, J., and Civas, A. (1995) Nucleic Acids Res. 23, 5055-5063) is different from interferon-stimulated gene factor 3. It binds to the D motif but not to the virus-unresponsive form of the D motif disrupted by a G-57 --> C substitution. We show that the low levels of IFN-A11 gene expression are caused essentially by the lack of two inducible enhancer domains disrupted by the A-78 --> G and the G-57 --> C substitutions. These data suggest a model taking account of the differential regulation of IFN-A gene family members. They also suggest that virus-induced factor may correspond to the primary transcription factor directly activated by virus that is involved in the initiation of IFN-A gene transcription.

Differential expression of c-jun and c-myc in N-nitroso diethylamine-induced hepatic oncogenesis in AKR mice

Expression of c-jun, c-myc, c-fos and c-Ha-ras was examined and correlated with the various stages of N-nitrosodiethylamine (NDEA)-induced hepatocarcinogenesis in male AKR mice. The treated groups were given NDEA 100 ppm, in drinking water for 120 days. The histopathology along with the expression of oncogenes were studied at different durations of treatment such as after 1 day, 3 days, 6 days, 9 days, 15 days, 20 days 30 days, 60 days, 90 days and 120 days of treatment. The results of histological investigation indicate mild hyperplasia and anisonucleosis at 30 days of treatment and prominent pathological features from 60 days onwards until the appearance of hepatocarcinoma at 120 days even without the development of any preneoplastic or neoplastic nodule. The results of the Northern blot hybridization clearly indicate an increased expression of c-jun from 15 days onwards. This overexpression of c-jun at such an early stage indicates its association with the events earlier than the neoplastic changes. However, the persistent overexpression of c-jun at all durations of treatment indicates its association with the events during the later stage of hepatocarcinogenesis, whereas c-myc overexpression starts from 30 days of treatment and persists until the end of the experiment, i.e. 120 days of treatment. However, the results of densitometric quantification indicate that the extent of increase expression of c-myc is less than that of c-jun expression until 1 month of treatment, after which the induction of c-myc exceeds the expression of c-jun. Thus, the overexpression of c-myc from 2 months onwards might be playing a critical role in maintenance of the malignant phenotype. On the other hand, the expressions of c-fos and c-Ha-ras do not have any alteration during NDEA treatment. Thus, our data demonstrate the involvement of c-jun and c-myc in NDEA-induced hepatocarcinogenesis in AKR mice.

The nuclear factor YY1 suppresses the human gamma interferon promoter through two mechanisms: inhibition of AP1 binding and activation of a silencer element

Our group has previously reported that the nuclear factor Yin-Yang 1 (YY1), a ubiquitous DNA-binding protein, is able to interact with a silencer element (BE) in the gamma interferon (IFN-gamma) promoter region. In this study, we demonstrated that YY1 can directly inhibit the activity of the IFN-gamma promoter by interacting with multiple sites in the promoter. In cotransfection assays, a YY1 expression vector significantly inhibited IFN-gamma promoter activity. Mutation of the YY1 binding site in the native IFN-gamma promoter was associated with an increase in the IFN-gamma promoter activity. Analysis of the DNA sequences of the IFN-gamma promoter revealed a second functional YY1 binding site (BED) that overlaps with an AP1 binding site. In this element, AP1 enhancer activity was suppressed by YY1. Since the nuclear level of YY1 does not change upon cell activation, our data support a model that the nuclear factor YY1 acts to suppress basal IFN-gamma transcription by interacting with the promoter at multiple DNA binding sites. This repression can occur through two mechanisms: (i) cooperation with an as-yet-unidentified AP2-like repressor protein and (ii) competition for DNA binding with the transactivating factor AP1.

Identification of distal silencing elements in the murine interferon-A11 gene promoter

The murine interferon-A11 (Mu IFN-A11) gene is a member of the IFN-A multigenic family. In mouse L929 cells, the weak response of the gene's promoter to viral induction is due to a combination of both a point mutation in the virus responsive element (VRE) and the presence of negatively regulating sequences surrounding the VRE. In the distal part of the promoter, the negatively acting E1E2 sequence was delimited. This sequence displays an inhibitory effect in either orientation or position on the inducibility of a virus-responsive heterologous promoter. It selectively represses VRE-dependent transcription but is not able to reduce the transcriptional activity of a VRE-lacking promoter. In a transient transfection assay, an E1E2-containing DNA competitor was able to derepress the native Mu IFN-A11 promoter. Specific nuclear factors bind to this sequence; thus the binding of trans-regulators participates in the repression of the Mu IFN-A11 gene. The E1E2 sequence contains an IFN regulatory factor (IRF)-binding site. Recombinant IRF2 binds this sequence and anti-IRF2 antibodies supershift a major complex formed with nuclear extracts. The protein composing the complex is 50 kDa in size, indicating the presence of IRF2 or antigenically related proteins in the complex. The Mu IFN-A11 gene is the first example within the murine IFN-A family, in which a distal promoter element has been identified that can negatively modulate the transcriptional response to viral induction.

A regulatory domain within the virus-response element of the interferon alpha 1 gene acts as a transcriptional repressor sequence and determinant of cell-specific gene expression

Type-I interferons are encoded by a multigene family, the major members of which are at least 13 IFN A subtypes and a single IFN B gene. IFNs A and B are induced in response to similar stimuli, such as virus infection and double-stranded RNA, but in different cell types: the induction of IFN A is almost exclusively restricted to cells of lymphoid origin, while IFN B has been found to be induced in a variety of cell types including fibroblasts. The virus-responsive enhancer element in the promoter region of IFN A family members is largely responsible for the differential expression of individual subtypes in responsive cells. In this paper we describe experiments which address the issue of the differential expression of IFN A and IFN B in different cell types. We show that IFN-beta is induced in a variety of cells of different origin, while not all of these are able to secrete IFN-alpha. By transfection of reporter gene constructs comprising the virus-responsive enhancer from the IFN A1 and IFN B genes, we show that this differential response is mediated at the level of transcription via these control elements. More detailed analysis of the function of these regions identifies specific sequences within the IFN A1 virus response element that has an inhibitory effect on expression in cells that are normally inducible, and is also implicated in the overall suppression of IFN A induction in non-inducible cells.

A novel PRD I and TG binding activity involved in virus-induced transcription of IFN-A genes

Comparative analysis of the inducible elements of the mouse interferon A4 and A11 gene promoters (IE-A4 and IE-A11) by transient transfection experiments, DNase 1 footprinting and electrophoretic mobility shift assays resulted in identification of a virus-induced binding activity suggested to be involved in NDV-induced activation of transcription of these genes. The virus-induced factor, termed VIF, is activated early by contact of virions with cells. It specifically recognizes the PRD I-like domain shared by both inducible elements, as well as the TG-like domain of IE-A4. This factor, distinct from the IRF-1, IRF-2 and the alpha F1 binding proteins and presenting a different affinity pattern from that of the TG protein, is proposed as a candidate for IFN-type I gene regulation.

Somatodendritic expression of an immediate early gene is regulated by synaptic activity

Trans-synaptic activation of gene expression is linked to long-term plastic adaptations in the nervous system. To examine the molecular program induced by synaptic activity, we have employed molecular cloning techniques to identify an immediate early gene that is rapidly induced in the brain. We here report the entire nucleotide sequence of the cDNA, which encodes an open reading frame of 396 amino acids. Within the hippocampus, constitutive expression was low. Basal levels of expression in the cortex were high but can be markedly reduced by blockade of N-methyl-D-aspartate receptors. By contrast, synaptic activity induced by convulsive seizures increased mRNA levels in neurons of the cortex and hippocampus. High-frequency stimulation of the perforant path resulted in long-term potentiation and a spatially confined dramatic increase in the level of mRNA in the granule cells of the ipsilateral dentate gyrus. Transcripts were localized to the soma and to the dendrites of the granule cells. The dendritic localization of the transcripts offers the potential for local synthesis of the protein at activated postsynaptic sites and may underlie synapse-specific modifications during long-term plastic events.

Differential constitutive expression of interferon genes in early mouse embryos

Recent evidence suggests that several processes during mammalian embryogenesis may be regulated by IFNs or IFN-like molecules. With the use of MAPPing, the simultaneous presence of transcripts homologous to IFN-alpha, IFN-beta, IRF-1, and IRF-2 was examined in mouse embryos and in embryonal carcinoma (EC) P19 cells, which are equivalent to epiblast cells of the early postimplantation blastocysts. Transcripts for IFN-alpha, but not for IFN-beta, were detected as maternal transcripts in the ovulated oocyte and persisted over early embryogenesis. IRF-1 transcripts appeared only after the first cell cleavage in the two-cell stage embryo. IRF-2 transcripts were analyzed only in EC P19 cells and were found in both undifferentiated (D-) and differentiated (D+) cells. The IFN-alpha transcripts present in (D-) P19 cells were cloned and the partial cDNA sequences determined. Mu IFN-alpha A and a new Mu IFN-alpha species (Mu IFN-alpha 12) were isolated from (D-) P19 cells. The presence of constitutive IFN-alpha transcripts in early mouse embryos suggests a role for these molecules during embryogenesis.

Cytokine production by normal human monocytes: inter-subject variation and relationship to an IL-1 receptor antagonist (IL-1Ra) gene polymorphism

Monocytes from different individuals show variable cytokine production in response to a variety of stimuli. We wished to determine the sets of conditions (cytokine combinations) that would enable us to demonstrate stable inter-individual differences in the production of IL-1 alpha, IL-1 beta, IL-1Ra, on-6 and tumour necrosis factor-alpha (TNF-alpha) by monocytes. We assessed the ability of a number of recombinant human cytokines (granulocyte-macrophage colony-stimulating factor (GM-CSF), interferon-gamma (IFN-gamma), TNF-alpha, IL-4, IL-6, transforming growth factor-beta (TGF-beta), IL-10 and IL-1Ra)) to stimulate or inhibit the production of one or more of these monocyte products. GM-CSF was found to stimulate the production of all five of these cytokines in a highly reproducible manner. TNF-alpha also up-regulated production of IL-1 alpha, IL-1 beta, IL-1Ra and IL-6 by monocytes, but the variability in the results of cells cultured from the same individuals on different occasions was greater. Other cytokines either stimulated production of only some of the five cytokine products tested, or stimulated the production of some cytokine products while inhibiting production of others. This was especially evident when cytokines were used in combination with GM-CSF: IFN-gamma down-regulated production of IL-1Ra while up-regulating the production of IL-1 alpha/beta, IL-6 and TNF-alpha, while IL-4 had the exact opposite effect. Polymorphisms in regions of cytokine genes that affect transcription may account for some of the interindividual variation in cytokine production. We have shown that a stable estimate of cytokine production phenotype can be obtained when monocytes collected on at least two separate occasions are stimulated by GM-CSF in vitro. We have looked for a relationship between IL-1 production and an 86-bp variable repeat polymorphism in intron 2 of the IL-1Ra gene. A less common allele of this polymorphism (allele 2) was associated with increased production of IL-1Ra protein, and also reduced production of IL-1 alpha protein by monocytes.

NF-kappa B-independent activation of beta-interferon expression in mouse F9 embryonal carcinoma cells

We have examined the behaviour of the beta-interferon promoter in mouse F9 embryonal carcinoma cells. In undifferentiated cells, the beta-interferon promoter is not responsive to dsRNA or to Sendai virus. In cells stimulated to differentiate into parietal endoderm by treatment with retinoic acid, the beta-interferon promoter responds to both inducers, but only Sendai virus can activate the transcription factor NF-kappa B previously thought to be essential for beta-interferon induction. Differentiated F9 cells therefore present an unprecedented situation in which induction of the beta-interferon gene does not require NF-kappa B. In addition to these differences, induction by dsRNA, but not by Sendai virus, is significantly enhanced by a pretreatment with interferon (priming). These observations suggest that paramyxo-viruses can participate in beta-interferon induction in a manner that is distinct from a simple generator of dsRNA. Analysis of the promoter requirements for induction in differentiated F9 cells suggests that induction is brought about by a novel mechanism using the currently identified regulatory domains.

A novel member of the interferon receptor family complements functionality of the murine interferon gamma receptor in human cells

Expression of the human interferon gamma receptor (IFN-gamma R) in mouse cells is not sufficient to confer biological responsiveness to human IFN-gamma and vice versa. An additional species-specific component is required for signal transduction. We identified this cofactor by expression cloning in simian COS cells stably transfected with the nonfunctional murine IFN-gamma R and a IFN-gamma-inducible reporter construct encoding the human Tac antigen (interleukin-2 receptor alpha chain, CD25). A cDNA clone was obtained that, upon stable transfection, rendered human HEp-2 cells expressing the murine IFN-gamma R fully responsive to murine IFN-gamma. This cDNA encodes a novel 332 amino acid type I transmembrane protein that belongs to the IFN receptor family and that we designate IFN-gamma R beta chain.

Polymorphism in human IL-1 receptor antagonist gene intron 2 is caused by variable numbers of an 86-bp tandem repeat

We have investigated the polymorphism in intron 2 of the interleukin-1 receptor antagonist gene and identified two new alleles of the system. We have shown that the polymorphism is caused by the variable copy number of an 86-bp sequence, by using the polymerase chain reaction and primers immediately flanking the repeat region, and by direct sequencing. The repeat region contains three potential protein-binding sites and therefore the variable copy number may have functional significance.

Characterization of the mouse type X collagen gene

Type X collagen, a homotrimer of alpha 1 (X) polypeptide chains, is specifically expressed by hypertrophic chondrocytes in regions of cartilage undergoing endochondral ossification. We have previously characterized a genomic clone containing the major part of the mouse type X collagen gene (col10a1) and assigned the locus for col10a1 to mouse chromosome 10 (Apte et al., Eur. J. Biochem. 224: 217-224, 1992). In this paper, through additional characterization of cDNA and genomic clones, we describe the complete organization of the col10a1 gene. The col10a1 gene is 7.2 kb in size and, as in the chick, col10a1 gene transcripts are generated from only three exons. Exon 1 encodes only the 5' untranslated (5' UT) region of the mRNA and is separated from exon 2 by an intron 562 bp in length. Exon 2 (169 bp) encodes 15 bp of 5' UT message, the translation start plus 17-amino acid residues of the putative signal peptide, and 33 1/3 codons of the putative N-terminal non-collagenous (NC2) domain of type X collagen. Exon 3 is 2854 bp in size and encodes 4 2/3 codons of the NC2 domain, the entire collagenous domain of 463 residues (COL), the entire C-terminal non-collagenous (NC1) domain (161 amino acid residues) and the entire 965 bp 3' untranslated (3' UT) sequence of the mRNA. Two TATA boxes are present in tandem in the col10a1 promotor. Both TATA boxes are active in transcription, generating two populations of transcripts with different 5'-termini; the longer transcript is of low abundance and is detectable only by PCR in newborn mice. The col10a1 promotor contains a CCAAT box as well as other consensus sequence elements required for binding of potential transcription factors. Characterization of the col10a1 gene provides data essential for studies of the regulation of type X collagen expression during mammalian endochondral bone growth and development. Knowledge of the complete structure of the mouse type X collagen gene will also be useful for the investigation of type X collagen gene abnormalities in murine chondrodysplasias and for the generation of transgenic mice.

A novel interferon-inducible domain: structural and functional analysis of the human interferon regulatory factor 1 gene promoter

We have cloned and functionally characterized the human interferon regulatory factor 1 (IRF-1) gene promoter. The promoter contains a CpG island, with several GC boxes, a CAAT box, but no TATA box. IRF-1 mRNA is strongly induced by gamma interferon (IFN-gamma) but more weakly and transiently by IFN-alpha. There are several putative kappa B motifs and numerous AA(G/A)G(G/T)A and GAAANN motifs throughout the promoter. The IRF-1 promoter is not autoregulated by the IRF-1 gene product. IFN inducibility of the promoter was studied with 5' deletion mutants linked to a heterologous reporter gene. Gel mobility shift assays were used to show IFN-inducible factor binding to the IRF-1 promoter. These studies showed that IFN inducibility is conferred by a novel imperfect inverted-repeat arrangement of two GAAANN motifs within a domain, 130 nucleotides upstream of transcription initiation. This inverted repeat binds a factor upon induction with IFN and can confer IFN inducibility on a heterologous promoter. Conversely, point mutations of the inverted repeat are not IFN inducible when linked to the same heterologous promoter.

A novel interferon-inducible domain: structural and functional analysis of the human interferon regulatory factor 1 gene promoter

We have cloned and functionally characterized the human interferon regulatory factor 1 (IRF-1) gene promoter. The promoter contains a CpG island, with several GC boxes, a CAAT box, but no TATA box. IRF-1 mRNA is strongly induced by gamma interferon (IFN-gamma) but more weakly and transiently by IFN-alpha. There are several putative kappa B motifs and numerous AA(G/A)G(G/T)A and GAAANN motifs throughout the promoter. The IRF-1 promoter is not autoregulated by the IRF-1 gene product. IFN inducibility of the promoter was studied with 5' deletion mutants linked to a heterologous reporter gene. Gel mobility shift assays were used to show IFN-inducible factor binding to the IRF-1 promoter. These studies showed that IFN inducibility is conferred by a novel imperfect inverted-repeat arrangement of two GAAANN motifs within a domain, 130 nucleotides upstream of transcription initiation. This inverted repeat binds a factor upon induction with IFN and can confer IFN inducibility on a heterologous promoter. Conversely, point mutations of the inverted repeat are not IFN inducible when linked to the same heterologous promoter.

Long-term sensitization training in Aplysia leads to an increase in the expression of BiP, the major protein chaperon of the ER

Long-term memory for sensitization of the gill- and siphon-withdrawal reflexes in Aplysia californica requires RNA and protein synthesis. These long-term behavioral changes are accompanied by long-term facilitation of the synaptic connections between the gill and siphon sensory and motor neurons, which are similarly dependent on transcription and translation. In addition to showing an increase in over-all protein synthesis, long-term facilitation is associated with changes in the expression of specific early, intermediate, and late proteins, and with the growth of new synaptic connections between the sensory and motor neurons of the reflex. We previously focused on early proteins and have identified four proteins as members of the immunoglobulin family of cell adhesion molecules related to NCAM and fasciclin II. We have now cloned the cDNA corresponding to one of the late proteins, and identified it as the Aplysia homolog of BiP, an ER resident protein involved in the folding and assembly of secretory and membrane proteins. Behavioral training increases the steady-state level of BiP mRNA in the sensory neurons. The increase in the synthesis of BiP protein is first detected 3 h after the onset of facilitation, when the increase in overall protein synthesis reaches its peak and the formation of new synaptic terminals becomes apparent. These findings suggest that the chaperon function of BiP might serve to fold proteins and assemble protein complexes necessary for the structural changes characteristic of long-term memory.

Long-term sensitization training in Aplysia leads to an increase in calreticulin, a major presynaptic calcium-binding protein

Long-term memory for sensitization in Aplysia requires new protein and RNA synthesis. Here, we identify a late protein as calreticulin, the major Ca(2+)-binding protein of the lumen of the endoplasmic reticulum. An antiserum against Aplysia calreticulin reveals an enrichment of calreticulin immunoreactivity in presynaptic varicosities. Quantitative S1 nuclease analysis indicates that the steady-state level of calreticulin mRNA in Aplysia sensory neurons increases during the maintenance phase of long-term sensitization. The finding that this mRNA increases in expression late, some time after training, is consistent with the idea that long-term neuromodulatory changes underlying sensitization may depend on a cascade of gene expression in which the induction of early regulatory genes leads to the expression of late effector genes.

Regulatory elements and transcriptional regulation by testosterone and retinoic acid of the rat nerve growth factor receptor promoter

The low-affinity nerve growth factor receptor (LNGFR) is a membrane-associated glycoprotein which is thought to participate in some of the biological activities of nerve growth factor (NGF). Expression of the LNGFR gene is known to be regulated both during development and in response to various agents in cell culture. However, molecular mechanisms responsible for the regulation have not been described. We report here an analysis of a 4.8-kb sequence from the 5'-flanking region of the rat LNGFR gene. Several regulatory elements were identified in this region by transfection of plasmid constructs containing sequences from LNGFR fused to a bacterial cat reporter gene. The proximal part of the promoter region (0.4-kb) was shown to be sufficient to support cat expression in all cell types used. A silencer element located between -1.5 kb and -1.8 kb from the start of translation, as well as an enhancer element in more upstream regions of the promoter, were identified in the phaeochromocytoma cell line, PC12, and in the Sertoli cell line, TM4, that express the LNGFR gene. Treatment of TM4 cells with retinoic acid (RA) increases the level of LNGFR mRNA twofold, while testosterone treatment results in a tenfold decrease. Regions of the promoter responsive to testosterone and RA in TM4 cells were found at -610 to -860 bp and -1840 to -4800 bp upstream from the translation start codon, respectively. A RA-responsive element active in PC12 cells is located between bp -610 to -860 from the start codon.

Inducible processing of interferon regulatory factor-2

PRDI-BFc and PRDI-BFi are proteins that bind specifically to a regulatory element required for virus induction of the human beta interferon (IFN-beta). PRDI-BFc is a constitutive binding activity, while the PRDI-BFi binding activity is observed only after cells are treated with inducers such as virus or poly(I).poly(C) plus cycloheximide or in some cells by cycloheximide alone. In this paper we report that PRDI-BFc is interferon regulatory factor-2 (IRF-2), a known transcriptional repressor. In addition, we find that PRDI-BFi is a truncated form of IRF-2, lacking approximately 185 C-terminal amino acids. Thus, PRDI-BFi appears to be generated by inducible proteolysis. Although the affinity of PRDI-BFc/IRF-2 for the IFN-beta promoter does not appear to be affected by the removal of C-terminal amino acids, the ability of PRDI-BFi to function as a repressor in cotransfection experiments is significantly less than that of intact IRF-2. Studies have shown that IRF-2 can block the activity of the transcriptional activator IRF-1, which also binds specifically to the IFN-beta gene promoter. Thus, the inducible proteolysis of IRF-2 may be involved in the regulation of the IFN-beta gene or of other genes in which the ratio of IRF-1 to IRF-2 can affect the level of transcription.

Inducible processing of interferon regulatory factor-2

PRDI-BFc and PRDI-BFi are proteins that bind specifically to a regulatory element required for virus induction of the human beta interferon (IFN-beta). PRDI-BFc is a constitutive binding activity, while the PRDI-BFi binding activity is observed only after cells are treated with inducers such as virus or poly(I).poly(C) plus cycloheximide or in some cells by cycloheximide alone. In this paper we report that PRDI-BFc is interferon regulatory factor-2 (IRF-2), a known transcriptional repressor. In addition, we find that PRDI-BFi is a truncated form of IRF-2, lacking approximately 185 C-terminal amino acids. Thus, PRDI-BFi appears to be generated by inducible proteolysis. Although the affinity of PRDI-BFc/IRF-2 for the IFN-beta promoter does not appear to be affected by the removal of C-terminal amino acids, the ability of PRDI-BFi to function as a repressor in cotransfection experiments is significantly less than that of intact IRF-2. Studies have shown that IRF-2 can block the activity of the transcriptional activator IRF-1, which also binds specifically to the IFN-beta gene promoter. Thus, the inducible proteolysis of IRF-2 may be involved in the regulation of the IFN-beta gene or of other genes in which the ratio of IRF-1 to IRF-2 can affect the level of transcription.

Distinct activation of murine interferon-alpha promoter region by IRF-1/ISFG-2 and virus infection

Virus infection in mouse L929 cells activates expression of interferon-alpha 4 (IFN-alpha 4), but not IFN-alpha 6. The integrity of a symmetrical sequence, GTAAAGAAAGT (alpha F1 site); (-103 to -93), present in the 35 nucleotide (nt) long inducible element (IE) (-109 to -75) of the alpha 4 promoter region is essential for the virus-induced expression. In the present study, we have shown that the interferon regulatory factor 1 (IRF-1) can induce expression of both IFN-alpha 4 and -alpha 6 in a transient expression assay. Virus infection cooperates with IRF-1 and further enhances transcription from the alpha 4 promoter, but inhibits the IRF-1-mediated expression from the alpha 6 promoter. The virus-mediated induction is determined by both IRF-1 and alpha F1 sites, while activation by IRF-1 in a cotransfection assay is not greatly influenced by the alpha F1 sequence. The activation of IFN-alpha gene promoters by IRF-1 was limited to the transient expression assay. The integrated alpha 4 promoter or the endogenous IFN-alpha genes could not be induced by transfection with IRF-1 expressing plasmid and IRF-1 did not up-regulate expression of the endogenous IRF-1 gene. However, expression of IRF-1 alone was sufficient to up-regulate the expression of two IFN stimulated genes, 2',5' oligoadenylate synthetase (OAS) and interferon stimulated (ISG)-15 gene. These results suggest that induction of IFN-alpha gene expression by virus infection requires cooperation between IRF-1 and another factor(s) that binds to the alpha F1 sequence.

Identification of novel factors that bind to the PRD I region of the human beta-interferon promoter

Treatment of cells with virus or synthetic double-stranded RNA (dsRNA) leads to the transient transcriptional activation of the beta-interferon gene. Genetic analysis has revealed that the 5' regulatory sequence responsible for this induction contains multiple positive and negative elements. One of these, Positive Regulatory Domain I (PRD I), has been shown to bind the positively-acting transcription factor IRF-1. In this study we show that this element is inducible under conditions where IRF-1 cannot be detected, suggesting that additional cellular factors are involved in the induction process. To investigate the existence of such factors we have analysed the range and properties of PRD I-binding activities present in HeLa cells. In addition to the repressor protein IRF-2, several novel factors can bind to PRD I in uninduced cells: two of these have properties consistent with a role in negative regulation; levels of two others increase upon priming, and may be alternative candidates for activators. Upon induction we also observe a novel factor whose appearance does not depend upon de novo protein synthesis, and which appears to be a truncated form of IRF-2. The potential involvement of these factors in regulating the beta-interferon gene is discussed.

Mx genes show weaker primary response to virus than other interferon-regulated genes

Some interferon (IFN)-regulated genes are induced as a primary response to virus as well as secondarily through virus-induced IFN. Here we investigated whether this dual control mechanism would also regulate the activity of the human and mouse Mx genes that encode proteins with intrinsic antiviral potentials. To distinguish between a primary response to virus and a secondary response to virus-induced IFN, we studied virus-induced Mx gene expression in cell lines that lack a functional IFN system and in cells with blocked protein synthesis. In contrast to the two IFN-regulated human genes ISG56 and ISG15, the human MxA gene showed almost no primary response to Newcastle disease virus (NDV) or influenza virus. Similarly, direct activation of the mouse Mx1 gene by NDV or influenza virus was not significant in mouse embryo cells or explanted peritoneal macrophages. A moderate primary Mx1 response to NDV was observed in the permanent cell line L1210. Lack of a strong IFN-independent Mx response to virus indicates that this mode of gene regulation does not play a significant role in Mx-mediated resistance to viral disease.

The porcine family of interferon-omega: cloning, structural analysis, and functional studies of five related genes

We report the molecular characterization of the porcine IFN-omega multigenic family which appears to comprise six to seven loci. Five of these loci were cloned and sequenced, revealing two pseudogenes (psi PoIFN-omega 1 and -omega 2) and three genes with an intact reading frame (PoIFN-omega 3, -omega 4, and -omega 5) that could encode preproteins of 179-190 amino acids including a putative signal peptide of 23 residues. By comparison of porcine IFN-omega coding sequences to those of known mammalian counterparts, it appeared that porcine sequences contain an in-frame five-codon deletion (between positions 113 and 117) in a region of relatively high sequence variability. In vitro transcription and translation of the three potentially functional reading frames gave rise to proteins with antiviral activity, showing that the porcine-specific deletion does not abolish the biological activity. Comparative analysis of flanking sequences revealed unique features of the 3' untranslated region of IFN-omega 4 gene: It contained a consensus estrogen-responsive element (ERE) in the vicinity of an extensive A-T-rich sequence known to serve a specific regulatory role in the expression of many genes involved in the inflammatory response. This finding suggests that the expression of the functional members of the porcine IFN-omega family may be mediated through different mechanisms. The expression of these genes was studied by Northern blot analysis of mRNAs from pig conceptus (days 14-20). Five bands of poly(A)+ RNAs hybridized with an IFN-omega probe provided the stringency was low, suggesting that a distinct family of IFN-omega-related genes were expressed by porcine trophoblastic cells during early gestation.

Activation of IFN-beta element by IRF-1 requires a posttranslational event in addition to IRF-1 synthesis

Expression of the Type I IFN (i.e., IFN-alpha s and IFN-beta) genes is efficiently induced by viruses at the transcriptional level. This induction is mediated by at least two types of positive regulatory elements located in the human IFN-beta gene promoter: (1) the repeated elements which bind both the transcriptional activator IRF-1 and the repressor IRF-2 (IRF-elements; IRF-Es), and (2) the kappa B element (kappa B-E), which binds NF kappa B and is located between the IRF-Es and the TATA box. In this study we demonstrate that a promoter containing synthetic IRF-E, which displays high affinity for the IRFs can be efficiently activated by Newcastle disease virus (NDV). In contrast, such activation was either very weak or nil when cells were treated by IFN-beta or tumor necrosis factor-alpha (TNF-alpha), despite the fact they both efficiently induce de novo synthesis of the short-lived IRF-1 in L929 cells. In fact, efficient activation of the IRF-E apparently requires an event in addition to de novo IRF-1 induction, which can be elicited by NDV even in the presence of protein synthesis inhibitor, cycloheximide. Moreover, efficient activation of the IRF-E by NDV is specifically inhibited by the protein kinase inhibitor, Staurosporin. Hence our results suggest the importance of IRF-1 synthesis and post-translational modification event(s), possibly phosphorylation for the efficient activation of IRF-Es, which are otherwise under negative regulation by IRF-2.

Transcriptional regulation of interferon-stimulated genes

Interferons (IFN) stimulate the expression of a number of genes following interaction with specific high-affinity plasma membrane receptors. The products of these genes either singly or coordinately mediate the antiviral, growth inhibitory or immunoregulatory activities attributed to IFN. While the gene products in some cases have been well characterized, other IFN-regulated genes encode proteins whose functions have yet to be elucidated. A feature common to all IFN-stimulated genes characterized thus far is the presence of a DNA element which constitutes an IFN-responsive enhancer, usually present in the 5' upstream region of the genes. This element, termed interferon-stimulated response element (ISRE) binds a nuclear factor(s) translocated from the cytoplasm to the nucleus following IFN-receptor-triggered signal transduction. The binding of these factors to the ISRE represents the initiating event in stimulating RNA-polymerase-II-mediated transcription from IFN-responsive genes. Depending on the nature of the cells responding to IFN and the genes involved, induced transcription may be prolonged or rapidly terminated. The rapid termination of transcription is dependent in some cases on IFN-induced protein synthesis and also involves factor binding to the ISRE. Recent progress in detailing these events will be discussed including IFN-receptor interactions, signal-transduction pathways, comparing and contrasting IFN-regulated genes and elucidation of IFN-regulated factors.

Purkinje cell protein-2 regulatory regions and transgene expression in cerebellar compartments

The Purkinje cell protein 2 (Pcp-2) is expressed in cerebellar Purkinje cells and retinal bipolar neurons. To illuminate how Pcp-2 expression is restricted to only two neuronal types and to derive tools to express heterologous genes in these neuronal subpopulations, genomic sequences of the mouse Pcp-2 gene have been cloned and flanking sequences have been evaluated as a source of neuron-specific regulatory elements. An upstream region with homology to other genes expressed in neurons was identified and a hybrid gene containing this sequence was constructed by ligating 0.4 kb of upstream and 0.3 kb of downstream Pcp-2-flanking DNA to lacZ. Transgenic mice bearing this construct exhibited beta-galactosidase in a wide array of neuron types, suggesting that this sequence may play an important role in specifying neuronal expression. Addition of a further 3.1 kb of Pcp-2 upstream sequences restricted expression of beta-galactosidase to a small number of neuron types and most notably to Purkinje cells within parasagitally oriented cerebellar compartments. The presence of elements lying within the 3.1-kb upstream region and acting to specifically restrict Pcp-2 expression is therefore suggested. Moreover, as beta-galactosidase was not expressed in the bipolar cells of these transgenic mice, retinal expression of the endogenous Pcp-2 gene must involve elements in addition to those conferring expression within Purkinje cells.

Identification and characterization of a novel repressor of beta-interferon gene expression

We have identified and characterized a novel repressor of human beta-interferon (beta-IFN) gene expression. This protein, designated PRDI-BF1, binds specifically to the PRDI element of the beta-IFN gene promoter and is distinct from previously reported proteins that bind to this sequence. PRDI-BF1 is an 88-kD protein containing five zinc-finger motifs. Cotransfection experiments in cultured mammalian cells revealed that PRDI-BF1 is a potent repressor of PRDI-dependent transcription. PRDI-BF1 blocks virus induction of the intact beta-IFN gene promoter and of synthetic promoters containing multiple PRDI sites. PRDI-BF1 can also block the SV40 enhancer when PRDI sites are located between the enhancer and the promoter. This repression is highly dependent on the location of the PRDI sites, however, indicating that PRDI-BF1 cannot act at a distance. On the basis of the properties of PRDI-BF1 and the observation that PRDI-BF1 mRNA accumulation is virus inducible, we propose that PRDI-BF1 may act as a postinduction repressor of the beta-IFN gene by displacing positive regulatory proteins from the PRDI site of the promoter.