Nuclear factors binding to the human immunoglobulin heavy-chain gene enhancer

A novel enhancer RNA, Hmrhl, positively regulates its host gene, phkb, in chronic myelogenous leukemia

Noncoding RNAs are increasingly being accredited with key roles in gene regulation during development and disease. Here we report the discovery and characterization of a novel long noncoding RNA, Hmrhl, which shares synteny and partial sequence similarity with the mouse lncRNA, Mrhl. The human homolog, Hmrhl, transcribed from intron 14 of phkb gene, is 5.5 kb in size, expressed in all tissues examined and is associated with chromatin. Analysis of Hmrhl locus using ENCODE database revealed that it exhibits hallmarks of enhancers like the open chromatin configuration, binding of transcription factors, enhancer specific histone signature etc. in the K562 Chronic Myelogenous Leukemia (CML) cells. We compared the expression of Hmrhl in the normal lymphoblast cell line, GM12878, with that of K562 cells and lymphoma samples and show that it is highly upregulated in leukemia as well as several cases of lymphoma. Further, we validated the enhancer properties of Hmrhl locus in K562 cells with the help of ChIP-qPCR and Luciferase assay. Moreover, siRNA mediated down-regulation of Hmrhl in K562 cells leads to a concomitant down regulation of its parent gene, phkb, showing that Hmrhl functions as an enhancer RNA and positively regulates its host gene, phkb, in chronic myelogenous leukemia. This study is significant in view of the fact that a better understanding of mechanism of gene regulation under normal conditions and its perturbation in cancer could in turn help in its therapeutic intervention through molecular medicine/RNA based drug discovery.

Phosphorylation of poly(rC) binding protein 1 (PCBP1) contributes to stabilization of mu opioid receptor (MOR) mRNA via interaction with AU-rich element RNA-binding protein 1 (AUF1) and poly A binding protein (PABP)

Gene regulation at the post-transcriptional level is frequently based on cis- and trans-acting factors on target mRNAs. We found a C-rich element (CRE) in mu-opioid receptor (MOR) 3'-untranslated region (UTR) to which poly (rC) binding protein 1 (PCBP1) binds, resulting in MOR mRNA stabilization. RNA immunoprecipitation and RNA EMSA revealed the formation of PCBP1-RNA complexes at the element. Knockdown of PCBP1 decreased MOR mRNA half-life and protein expression. Stimulation by forskolin increased cytoplasmic localization of PCBP1 and PCBP1/MOR 3'-UTR interactions via increased serine phosphorylation that was blocked by protein kinase A (PKA) or (phosphatidyl inositol-3) PI3-kinase inhibitors. The forskolin treatment also enhanced serine- and tyrosine-phosphorylation of AU-rich element binding protein (AUF1), concurrent with its increased binding to the CRE, and led to an increased interaction of poly A binding protein (PABP) with the CRE and poly(A) sites. AUF1 phosphorylation also led to an increased interaction with PCBP1. These findings suggest that a single co-regulator, PCBP1, plays a crucial role in stabilizing MOR mRNA, and is induced by PKA signaling by conforming to AUF1 and PABP.

Molecular characterization of the Pb recombination hotspot in the mouse major histocompatibility complex class II region

In the mouse major histocompatibility complex (MHC) class II region, meiotic recombination breakpoints are clustered in four specific sites known as hotspots. Here we reveal the primary structure of a hotspot near the Pb gene. A total of 12 crossover points were found to be confined to a 15-kb DNA segment of the Pb pseudogene. Moreover, the crossover points are concentrated in a 341-bp segment, which includes a part of exon 4 and intron 4 of the Pb gene. All four MHC hotspots appear to be located within genes or at the 3' end of genes, contrasting with characterized hotspots in budding yeast, which are mostly located at the 5'-promoter regions of genes. The Pb hotspot has several consensus motifs, an octamer transcription factor-binding sequence, the B-motif-like transcription factor-binding sequence, and tandem repeats of tetramer sequence-all of which are shared by the other three hotspots. Systematic analysis of the public database demonstrated that the full motif set occurs rarely in the nucleotide sequence of the entire MHC class II region. All results suggest that the motif set has an indispensable role in determining their site specificity.

Human HE2 (microB) and microA motifs show the same function as whole IgH intronic enhancer in transgenic mice

In the murine IgH gene intronic enhancer (ENHiH), two major functional domains were reported. One is the E4/octomer region and another includes the microA and microB motifs. In the human ENHiH, it was reported that the HE2, which corresponds to the murine microB, and E6 motifs play an important role in an enhancer activity and a tissue-specificity at cellular level. Here we examined the in vivo function of the E6, microA and HE2 motifs within the human ENHiH by using the transgenic mice technique. The microA and HE2 motifs together revealed almost the same enhancer function as the whole human ENHiH, but the E6 motif had lesser enhancer activity and tissue-specificity.

Pi, a pre-B-cell-specific enhancer element in the immunoglobulin heavy-chain enhancer

We have identified a new immunoglobulin heavy-chain enhancer element, designated pi, between the microE2 and microE3 elements. The pi enhancer element is transcriptionally active primarily during early stages of B-cell development but becomes virtually inactive during B-cell maturation at about the stage of immunoglobulin kappa light-chain gene rearrangement. Mutational analysis suggests that the pi element is crucial for immunoglobulin heavy-chain enhancer activity at the pre-B-cell stage but is almost irrelevant for enhancer activity at the mature B-cell or plasma-cell stage. The activity of the pi enhancer element correlates with the presence of an apparently pre-B-cell-specific protein-DNA complex. The similarity of the pi site to recognition sequences for members of the ets gene family suggests that the protein(s) interacting with the pi site most likely are ets-related transcription factors.

Pi, a pre-B-cell-specific enhancer element in the immunoglobulin heavy-chain enhancer

We have identified a new immunoglobulin heavy-chain enhancer element, designated pi, between the microE2 and microE3 elements. The pi enhancer element is transcriptionally active primarily during early stages of B-cell development but becomes virtually inactive during B-cell maturation at about the stage of immunoglobulin kappa light-chain gene rearrangement. Mutational analysis suggests that the pi element is crucial for immunoglobulin heavy-chain enhancer activity at the pre-B-cell stage but is almost irrelevant for enhancer activity at the mature B-cell or plasma-cell stage. The activity of the pi enhancer element correlates with the presence of an apparently pre-B-cell-specific protein-DNA complex. The similarity of the pi site to recognition sequences for members of the ets gene family suggests that the protein(s) interacting with the pi site most likely are ets-related transcription factors.

Multiple negative elements in a gene that codes for an extracellular matrix protein, collagen X, restrict expression to hypertrophic chondrocytes

During skeletal development, chondrocytes go through several stages of differentiation. The last stage, chondrocyte hypertrophy, occurs in areas of endochondral ossification. Mature hypertrophic chondrocytes differ from immature chondrocytes in that they become postmitotic, increase their cellular volume up to eightfold, and synthesize a unique set of matrix molecules. One such molecule is a short collagenous protein, collagen X. Previous studies have shown that collagen X is not expressed by other cell types and that its specific expression in hypertrophic chondrocytes is controlled by transcriptional mechanisms. To define these mechanisms, plasmid constructs containing the chicken collagen X gene promoter and 5' flanking regions fused to a reporter gene (chloramphenicol acetyl transferase, CAT) were transfected into primary cultures of collagen X-expressing and nonexpressing cells. A construct containing a short (558 bp) promoter exhibited high levels of CAT activity in all cell types (fibroblasts, immature, and hypertrophic chondrocytes). Adding a 4.2-kb fragment of 5' flanking DNA to this construct resulted in a dramatic reduction of CAT activity in fibroblasts and immature chondrocytes, but had no effect in hypertrophic chondrocytes. Addition of three subfragments of the 4.2-kb fragment to the initial construct, either individually or in various combinations, showed that all subfragments reduced CAT activity somewhat in non-collagen X-expressing cells, and that their effects were additive. Unrelated DNA had no effect on CAT activity. The results suggest that multiple, diffuse upstream negative regulatory elements act in an additive manner to restrict transcription of the collagen X gene to hypertrophic chondrocytes.

The mouse Eb meiotic recombination hotspot contains a tissue-specific transcriptional enhancer

A meiotic recombination hotspot exists within the second intron of the mouse major histocompatibility complex (MHC) gene, Eb. In the present study, a small fragment from the intron which contains two potential transcriptional regulatory elements was cloned into an expression vector and its effect on transcription was tested. This fragment was found to contain tissue-specific transcriptional enhancer activity. An octamer-like sequence and a B motif may contribute to this enhancer activity. Similar regulatory sequences with the same orientation and distance from one another are found in another mouse MHC recombination hotspot.

Structural and functional identification of regulatory regions and cis elements surrounding the nerve growth factor gene promoter

The transcriptional mechanisms which contribute to the regulation of nerve growth factor (NGF) production are still largely unknown. We previously expressed the NGF promoter region in transgenic mice to localize cis regulatory elements to within 5 kb of the promoter. To further map these elements, and to begin to study the corresponding transacting factors, we here assayed the effects of 5' deletions and point mutations and examined the binding of nuclear factors to the NGF promoter region using L929 cell fibroblasts. Sequential deletions delineated regions upstream from the promoter which stimulated and inhibited transcription. DNAse-1 footprinting experiments identified four upstream segments, designated F2, F4, F6 and F8, which bound L929 cell nuclear proteins. F2 and F4 mapped to stimulatory and F6 and F8 to inhibitory regions. Competition experiments using a heptanucleotide present in both F2 and F4 segments suggested that they may be bound by related factors. Gel shift assays showed that the F8 binding proteins are less abundant in L929 cells than in NIH 3T3 fibroblasts and B16 melanoma cells. In addition to the upstream segments, a downstream AP-1 consensus sequence bound L929 nuclear proteins. Mutation of the AP-1 consensus sequence eliminated binding of nuclear proteins and reduced transcriptional activity. Our results indicate that transcriptional activator as well as suppressor regions surround the NGF gene promoter. The regulation of NGF production is likely to involve cis elements within these regions and transacting factors that bind to them.

Expression of immunoglobulin genes in common variable immunodeficiency

Five common variable immunodeficiency (CVI) patients were analyzed for expression of immunoglobulin (Ig) genes. In the pokeweed mitogen (PWM)-induced Ig-production assay, the combination of T and B cells showed that all patients' T cells had normal helper functions and all patients' B cells had profound defects. The defective B-cell maturation stages based on their Ig gene expression patterns were variable. One of five patients showed normal mu-chain gene expression and nearly normal IgM production, but neither IgG nor IgA production, which suggested that this patient's B-cell defects might lie on a mu- to gamma or mu- to alpha class-switch stage. B cells in another patient showed low mu-chain gene expression and low IgM production, but an Ig enhancer region, which is an important region for expression of Ig genes, was intact. Thus, this patient might have a transacting factor defect which interacts with the Ig enhancer region. The other three patients showed no mu-chain gene expression and no IgM production. Thus, their B-cell defects lay on the B-cell maturation stage, similar to X-linked agammaglobulinemia. These results showed that primary B-cell defects in CVI occurred at several B-cell differentiation stages, which could be recognized by expression of Ig genes.

mRNA transcripts initiating within the human immunoglobulin mu heavy chain enhancer region contain a non-translatable exon and are extremely heterogeneous at the 5' end

Transcription events are thought to precede gene rearrangement in the immunoglobulin (Ig) loci and may be the mechanism by which the various gene regions are made accessible for recombination. If this is the case, identification and characterization of transcripts from the Ig loci should permit a better understanding of the gene rearrangement process. We have isolated a 2.3 kb cDNA clone from the human pre-B cell line Nalm-1 that contains enhancer-specific sequences from the Ig heavy (H) chain gene locus. The 2.3 kb transcript initiated within the enhancer region and showed extreme 5' heterogeneity, with more than 50 initiation sites mapping near the Ig-specific octamer ATTTGCGT. Sequencing of the cDNA clone demonstrated that 644 nucleotides from the Ig enhancer region were incorporated as a leader exon spliced to the mu constant (Cmu) region. This leader exon contained many translation termination codons and may function to inhibit the translation of sterile Cmu polypeptides. Using an enhancer-derived probe, we detected two low-abundancy mRNA transcripts with sizes of 2.3 and 12 kb. Northern blot analysis suggested that the 12 kb transcript was the unspliced precursor mRNA of a VDJ rearrangement. The potential role of these enhancer-containing transcripts in the opening of the IgH chain gene for rearrangement and for class switching is discussed.

DNase I-hypersensitive sites and transcription factor-binding motifs within the mouse E beta meiotic recombination hot spot

The second intron of the E beta gene in the mouse major histocompatibility complex is the site of a meiotic recombination hot spot. We detected two DNase I-hypersensitive sites in this intron in meiotic cells isolated from mouse testes. One site appears to be constitutive and is found in other tissues regardless of whether or not they express the E beta gene. Near this hypersensitive site are potential binding motifs for H2TF1/KBF1, NF kappa B, and octamer transcription factors. Gel retardation studies with mouse lymphoma cell nuclear extracts confirmed that each of these motifs is capable of binding protein. The binding of transcription factors may contribute to the enhancement of recombination potential by altering chromatin structure and increasing the accessibility of the DNA to the recombination machinery.

DNase I-hypersensitive sites and transcription factor-binding motifs within the mouse E beta meiotic recombination hot spot

The second intron of the E beta gene in the mouse major histocompatibility complex is the site of a meiotic recombination hot spot. We detected two DNase I-hypersensitive sites in this intron in meiotic cells isolated from mouse testes. One site appears to be constitutive and is found in other tissues regardless of whether or not they express the E beta gene. Near this hypersensitive site are potential binding motifs for H2TF1/KBF1, NF kappa B, and octamer transcription factors. Gel retardation studies with mouse lymphoma cell nuclear extracts confirmed that each of these motifs is capable of binding protein. The binding of transcription factors may contribute to the enhancement of recombination potential by altering chromatin structure and increasing the accessibility of the DNA to the recombination machinery.

Positive and negative regulation of immunoglobulin gene expression by a novel B-cell-specific enhancer element

A new B-cell-specific enhancer element has been identified 3' of E4 and the octamerlike motifs in the human immunoglobulin heavy-chain gene enhancer. Tandem copies of this 67-bp MnlI-AluI fragment, when fused to the chloramphenicol acetyltransferase gene driven by the conalbumin promoter, stimulated transcription in B cells but not in Jurkat T cells or HeLa cells. Footprinting analysis revealed that the identical sequence CCGAAACTGAAAAGG, designated E6, was protected by nuclear extracts from B cells, T cells, or HeLa cells. Gel mobility shift assays using a synthetic E6 motif detected a B-cell-specific complex in addition to a ubiquitous band found also in T cells and HeLa cells. In agreement with the results of gel retardation assays, tandem copies of the E6 motif stimulated transcription in ARH77 and Raji cells but not in Jurkat or HeLa cells. Furthermore, a mutant E6 motif lost both in vitro binding activity and in vivo enhancer activity. In striking contrast to the mouse Ig heavy-chain enhancer, in which the octamer motif acts as a B-cell-specific enhancer element, the human enhancer contains an octamerlike sequence with one base substitution which bound octamer-binding proteins with only very low affinity and showed no enhancer activity of its own. Interestingly, the MnlI-AluI fragment could suppress the basal-level activity of the conalbumin promoter in both Jurkat and HeLa cells. Moreover, simian virus 40 enhancer activity was blocked by the MnlI-AluI fragment in HeLa cells but not in B cells. Thus, the novel enhancer element identified in this study is probably a target site for both positive and negative factors.

Sequencing of selected regions of the human immunoglobulin heavy-chain gene locus that completes the sequence from JH through the delta constant region

Much of the nucleotide sequence between the start of the joining region and the end of the immunoglobulin heavy chain delta gene has already been determined. However, two gaps existed in potentially functionally important regions in this sequence: the region between the 3' end of the joining region and the heavy chain enhancer region and that between the enhancer and the mu constant region. We have determined the nucleotide sequences of these regions. The 734 bp between the joining and enhancer regions contained no additional joining regions. The 4525 bp region between the heavy chain enhancer and the mu constant region contains the mu switch region, which consists of pentameric repeats. Approximately 60% of these repeats are GGGCT and GAGCT. With the determination of these sequences, the entire region of the heavy chain locus starting upstream of the joining region to downstream of the last exon of the delta constant region (a total of more than 29 kb) has now been sequenced.

Positive and negative regulation of immunoglobulin gene expression by a novel B-cell-specific enhancer element

A new B-cell-specific enhancer element has been identified 3' of E4 and the octamerlike motifs in the human immunoglobulin heavy-chain gene enhancer. Tandem copies of this 67-bp MnlI-AluI fragment, when fused to the chloramphenicol acetyltransferase gene driven by the conalbumin promoter, stimulated transcription in B cells but not in Jurkat T cells or HeLa cells. Footprinting analysis revealed that the identical sequence CCGAAACTGAAAAGG, designated E6, was protected by nuclear extracts from B cells, T cells, or HeLa cells. Gel mobility shift assays using a synthetic E6 motif detected a B-cell-specific complex in addition to a ubiquitous band found also in T cells and HeLa cells. In agreement with the results of gel retardation assays, tandem copies of the E6 motif stimulated transcription in ARH77 and Raji cells but not in Jurkat or HeLa cells. Furthermore, a mutant E6 motif lost both in vitro binding activity and in vivo enhancer activity. In striking contrast to the mouse Ig heavy-chain enhancer, in which the octamer motif acts as a B-cell-specific enhancer element, the human enhancer contains an octamerlike sequence with one base substitution which bound octamer-binding proteins with only very low affinity and showed no enhancer activity of its own. Interestingly, the MnlI-AluI fragment could suppress the basal-level activity of the conalbumin promoter in both Jurkat and HeLa cells. Moreover, simian virus 40 enhancer activity was blocked by the MnlI-AluI fragment in HeLa cells but not in B cells. Thus, the novel enhancer element identified in this study is probably a target site for both positive and negative factors.

Identification of a novel factor that interacts with an immunoglobulin heavy-chain promoter and stimulates transcription in conjunction with the lymphoid cell-specific factor OTF2

The tissue-specific expression of the MOPC 141 immunoglobulin heavy-chain gene was studied by using in vitro transcription. B-cell-specific transcription of this gene was dependent on the octamer element 5'-ATGCAAAG-3', located in the upstream region of this promoter and in the promoters of all other immunoglobulin heavy- and light-chain genes. The interaction of purified octamer transcription factors 1 and 2 (OTF1 and OTF2) with the MOPC 141 promoter was studied by using electrophoretic mobility shift assays and DNase I footprinting. Purified OTF1 from HeLa cells and OTF1 and OTF2 from B cells bound to identical sequences within the heavy-chain promoter. The OTF interactions we observed extended over the heptamer element 5'-CTCAGGA-3', and it seems likely that the binding of the purified factors involves cooperation between octamer and heptamer sites in this promoter. In addition to these elements, we identified a second regulatory element, the N element with the sequence 5'-GGAACCTCCCCC-3'. The N element could independently mediate low levels of transcription in both B-cell and HeLa-cell extracts, and, in conjunction with the octamer element, it can promote high levels of transcription in B-cell extracts. The N element bound a transcription factor, NTF, that is ubiquitous in cell-type distribution, and NTF was distinct from any of the previously described proteins that bind to similar sequences. Based on these results, we propose that NTF and OTF2 interactions (both with their cognate DNA elements and possibly at the protein-protein level) may be critical to B-cell-specific expression and that these interactions provide additional pathways for regulating gene expression.

Identification of a novel factor that interacts with an immunoglobulin heavy-chain promoter and stimulates transcription in conjunction with the lymphoid cell-specific factor OTF2

The tissue-specific expression of the MOPC 141 immunoglobulin heavy-chain gene was studied by using in vitro transcription. B-cell-specific transcription of this gene was dependent on the octamer element 5'-ATGCAAAG-3', located in the upstream region of this promoter and in the promoters of all other immunoglobulin heavy- and light-chain genes. The interaction of purified octamer transcription factors 1 and 2 (OTF1 and OTF2) with the MOPC 141 promoter was studied by using electrophoretic mobility shift assays and DNase I footprinting. Purified OTF1 from HeLa cells and OTF1 and OTF2 from B cells bound to identical sequences within the heavy-chain promoter. The OTF interactions we observed extended over the heptamer element 5'-CTCAGGA-3', and it seems likely that the binding of the purified factors involves cooperation between octamer and heptamer sites in this promoter. In addition to these elements, we identified a second regulatory element, the N element with the sequence 5'-GGAACCTCCCCC-3'. The N element could independently mediate low levels of transcription in both B-cell and HeLa-cell extracts, and, in conjunction with the octamer element, it can promote high levels of transcription in B-cell extracts. The N element bound a transcription factor, NTF, that is ubiquitous in cell-type distribution, and NTF was distinct from any of the previously described proteins that bind to similar sequences. Based on these results, we propose that NTF and OTF2 interactions (both with their cognate DNA elements and possibly at the protein-protein level) may be critical to B-cell-specific expression and that these interactions provide additional pathways for regulating gene expression.

A novel B-cell lineage-specific transcription factor present at early but not late stages of differentiation

A novel B-cell-specific transcription factor, BSAP, was identified as a mammalian homolog of the sea urchin protein TSAP, which interacts with the promoters of four tissue-specific late histone H2A-2 and H2B-2 genes. As shown by mobility-shift, methylation interference, and mutational analyses, the mammalian protein BSAP recognizes all four sea urchin binding sites in a manner indistinguishable from TSAP; however, the two proteins differ in molecular weight. BSAP is exclusively restricted to the B-cell lineage of lymphoid differentiation. Its expression appears to be activated during pro-B-cell development, is abundant at the pre-B- and mature B-cell stages, but is absent in terminally differentiated plasma cells. Moreover, BSAP is clearly a B-cell-specific transcription factor, as a wild-type but not a mutant TSAP-binding site of the sea urchin functions only in transfected B cells as an upstream promoter element. Competition experiments did not reveal any high-affinity binding site for BSAP in known regulatory regions of immunoglobulin and class II major histocompatibility (MHC) genes, suggesting that BSAP is a regulator of a different set of B-lymphoid-specific genes.

B-cell control region at the 5' end of a major histocompatibility complex class II gene: sequences and factors

Transcription of major histocompatibility complex class II genes is elaborately regulated. Mouse class II genes are transcribed primarily in B cells, peripheral macrophages and interdigitating cells, and thymic cortical and medullary cells. In this study, we began to identify the DNA sequences and protein factors that control expression of a class II gene in B cells, addressing in particular how closely they resemble those that regulate immunoglobulin gene expression. We describe a region upstream of the E alpha gene that is crucial for its transcription in the B cells of transgenic mice but is less important in cultured B-cell lines. The sequence of this region reveals several familiar motifs, including a second X-Y pair reminiscent of that residing in the promoter-proximal region of all class II genes, a B motif strikingly homologous to that associated with the immunoglobulin kappa gene enhancer, several Ephrussi motifs, and a Pu box-like sequence very similar to that implicated in simian virus 40 and lymphotrophic papovavirus expression in B cells. Careful study of the proteins that bind specifically to these different motifs prompts us to suggest that major histocompatibility complex class II and immunoglobulin genes rely on quite different factors to achieve B-cell-specific expression.

B-cell control region at the 5' end of a major histocompatibility complex class II gene: sequences and factors

Transcription of major histocompatibility complex class II genes is elaborately regulated. Mouse class II genes are transcribed primarily in B cells, peripheral macrophages and interdigitating cells, and thymic cortical and medullary cells. In this study, we began to identify the DNA sequences and protein factors that control expression of a class II gene in B cells, addressing in particular how closely they resemble those that regulate immunoglobulin gene expression. We describe a region upstream of the E alpha gene that is crucial for its transcription in the B cells of transgenic mice but is less important in cultured B-cell lines. The sequence of this region reveals several familiar motifs, including a second X-Y pair reminiscent of that residing in the promoter-proximal region of all class II genes, a B motif strikingly homologous to that associated with the immunoglobulin kappa gene enhancer, several Ephrussi motifs, and a Pu box-like sequence very similar to that implicated in simian virus 40 and lymphotrophic papovavirus expression in B cells. Careful study of the proteins that bind specifically to these different motifs prompts us to suggest that major histocompatibility complex class II and immunoglobulin genes rely on quite different factors to achieve B-cell-specific expression.

Isolation of putative promoter region for human terminal deoxynucleotidyltransferase gene

We have isolated the genomic clone, which contained 5'-flanking region for human terminal deoxynucleotidyltransferase (TdT) gene, by screening Charon 4A library and determined its nucleotide sequence. Two transcription initiation sites (cap sites) were localized at 81 and 106 bp upstream from the third ATG codon which is translation initiation site, by primer extension analysis. Although neither typical TATA nor CAAT sequences were detected within 100 bp upstream region of the 5' cap site, a palindromic structure comprised of 28 bp was formed just upstream of the 5' cap site and double repeats of 5'-CTGGC sequence were found in its palindrom. The typical octamer of 5'-ATGCAAAT and three octamer-like sequences, which are involved in the transcription of lymphoid-specific genes, were detected at 212, 293, 347 and 770 bp upstream from the first cap site.

Mutational analysis of the contribution of sequence motifs within the IgH enhancer to tissue specific transcriptional activation

We have investigated the role of sequence motifs in the immunoglobulin heavy chain (IgH) enhancer on its activity in myeloma and fibroblast cell-lines. In transient transfection assays the transcription stimulatory activity of the enhancer is decreased in myeloma cells by mutating the E motifs 1, 2 and 3, the core motifs C1, C2, C3 and the octamer motif (OC) and in fibroblasts by mutating E2, E3, and C2. Our results suggest that transcription factors binding to E1, C1, C3 and OC contribute in a positive manner to the tissue specificity of the IgH enhancer.

Identification and partial purification of a protein binding to the human immunoglobulin kappa enhancer kappa E2 site

We previously described a domain in the 5' half of the human immunoglobulin kappa enhancer which could bind nuclear proteins in vitro, as detected by a lambda exonuclease protection assay. A second more 3' binding domain in the enhancer has now been detected by a similar assay employing a different exonuclease, the T7 gene 6 exonuclease. Using this assay and starting with a pig spleen nuclear extract, we have purified 5000-fold a protein that binds to the 3' domain. In a DNase I footprint experiment the partially purified protein protects a 27 bp segment in the enhancer centered around the sequence CAGGTGGC, which corresponds to the kappa E2 sequence motif described in the mouse kappa enhancer. The protein, designated NF-kappa E2, also appears to bind at a position downstream of kappa E2, at or near the kappa E3 site. Proteins capable of binding at kappa E2 are found in several mammalian species and are expressed in both lymphoid and non-lymphoid tissues.

Purification of a nuclear trans-acting factor involved in the regulated transcription of a human immunoglobulin heavy chain gene

The expression of the rearranged human immunoglobulin gamma 1 heavy chain gene (HIG1) was shown to be induced through its enhancer by the positive regulatory trans-acting factor(s) that was contained only in cells of B lineage. The trans-acting factors were purified from mouse myeloma NS1 cells, and HIG1-inducing activity was found mainly in fractions of molecular weight 53-127 kd and in a fraction eluted from a heparin-Sepharose column with 0.5 M KCI. This semipurified fraction contained proteins binding to the conserved octamer sequence, ATGCAAAT, in the promoter region, as well as to sequences in the enhancer region. The 0.5 M KCI eluates from a heparin-Sepharose column were applied to a DNA affinity column of synthetic oligonucleotides of the octamer sequence and the sequence TATTTTAGGAAGCAAA in the HpaII-BgIII region of the HIG1 gene enhancer. The protein eluted from the enhancer sequence-specific DNA affinity column showed a strong inducing activity for the HIG1 gene, and the molecular weight of a predominant protein was 96 kd.