c-myc expression is activated by the immunoglobulin kappa-enhancers from a distance of at least 30 kb but not by elements located within 50 kb of the unaltered c-myc locus in vivo

50 kb of contiguous DNA sequences covering the human c-myc coding region and approximately 20 kb of flanking upstream and downstream sequences were cloned onto a prokaryotic F-factor derived plasmid, which also contains a selectable marker and the plasmid origin of DNA replication oriP of Epstein Barr virus (EBV). Since these plasmids replicate extrachromosomally after stable transfection into EBV-positive B-cell lines, the gene regulation of c-myc can be analysed independent from chromosomal integration positions. Despite the presence of all known c-myc regulatory elements on these constructs, expression from the stably transfected c-myc gene was barely detectable in either cell line. Hypermethylation of these plasmids could be excluded as a mechanism for the lack of gene expression. Insertion of the immunoglobulin kappa-intron and 3' enhancers, however, activated c-myc transcription, when placed adjacent to or separated from the c-myc promoters by as far as 30 kb. These results indicate that transcription of c-myc in vivo requires additional and still unidentified control elements located outside this 50 kb fragment, and experimentally demonstrate long range enhancer function in vivo.

Among 17 inducers of differentiation only sodium butyrate causes a permanent down-regulation of c-myc in Burkitt's lymphoma

De-regulation of c-myc by chromosomal translocation is one crucial step for the development of Burkitt's lymphoma. The de-regulation is caused through juxtaposition of c-myc with one of the 3 immunoglobulin loci. We have reported earlier that treatment of Burkitt's lymphoma cells with n-butyrate causes transcriptional down-regulation of c-myc expression. Because of the possible therapeutic implication of this result, we looked for other compounds which, on the one hand, might be applicable in vivo and, on the other hand, might cause down-regulation of c-myc expression in Burkitt's lymphoma cells. Since n-butyrate is known to induce differentiation, we have examined other differentiation inducers of different chemical nature for their ability to reduce c-myc expression in Burkitt's lymphoma cells. Many of the substances tested caused down-regulation of c-myc expression, which, however, was transient except for n-butyrate. Three types of compounds proved to be particularly active: polar planar compounds (e.g., dimethylsulfoxide), heterocyclic compounds (e.g., hypoxanthine), and short-chain fatty acids (e.g., n-butyric acid). The action of n-butyrate on c-myc suppression was exceptional not only in not being transient, but also in being allele-specific: it down-regulated the translocated allele without affecting the normal one. Medium transfer experiments revealed that neither degradation of the active compound nor an intracellular resistance mechanism can fully account for the reversibility of c-myc down-regulation after treatment with the transiently acting polar planar compounds.

Characterization of macromolecular lignins as Epstein-Barr virus inducer in foodstuff associated with nasopharyngeal carcinoma risk

Epstein-Barr virus (EBV)-inducing activity was previously demonstrated to occur in various foodstuffs, including dried salted fish in southern China and 'harissa', a homemade spice mixture in Tunisia, whose consumption is epidemiologically associated with an increased risk for developing nasopharyngeal carcinoma (NPC). For the isolation and the characterization of active ingredients in harissa, we used as a rapid screening assay the induction of the chloramphenicol acetyltransferase (CAT) activity through the EBV-DR promoter in DR-CAT Raji cells. After fractionation of harissa and column chromatography on Sepharose-CL4B, the major inducing activity was associated with a macromolecular fraction which was chemically characterized as liginin-containing complexes. The active material enhanced EBV-DR induction with an activity comparable to the tumor promoter and strong EBV inducer, 12-O-tetradecanoylphorbol-13-acetate. Experiments with inhibitors of protein kinase C-related pathways suggested that the EBV-inducing activity of lignin fractions operates through a different pathway. Our results on the presence of specific lignin fractions in high-risk food items that can induce important cellular functions linked to tumor promotion are discussed in relation to NPC genesis and etiology.

The role of immunoglobulin kappa elements in c-myc activation

Burkitt's lymphoma cells are characterized by chromosomal translocations involving the proto-oncogene c-myc on chromosome 8 and one of the immunoglobulin gene loci on chromosome 2, 14 or 22. The translocated c-myc allele is transcriptionally activated, shows a preferential usage of promoter P1 over P2 (promoter shift) and lacks the ability to retain the transcription complex at the P2 promoter. In order to define the elements of the immunoglobulin kappa gene involved in deregulation of c-myc in a t(2;8) translocation, we designed constructs consisting of c-myc and different parts of the immunoglobulin kappa gene locus. Chromatin analysis of these stably transfected constructs revealed DNase I hypersensitive sites within the c-myc 5' region characteristic for an actively transcribed c-myc gene and three sites within the immunoglobulin kappa locus corresponding to the matrix attachment region, the intron and 3' enhancers, respectively. These three regulatory elements were necessary and sufficient for maximal c-myc activation and formation of the promoter shift. Kinetic nuclear run on experiments were performed to study the distribution of transcription complexes on c-myc exon 1 on constructs with and without the immunoglobulin kappa regulatory elements. The absence of a pausing polymerase complex at the c-myc P2 promoter could be demonstrated for constructs consisting of c-myc and the two kappa enhancers. Therefore the two enhancers are sufficient to relief the elongational block at the P2 promoter, however, the matrix attachment region is additionally required for maximal c-myc activation observed in Burkitt's lymphoma cells.

Identification of two enhancer elements downstream of the human c-myc gene

Expression of the proto-oncogene c-myc is tightly regulated in vivo. Transcription of c-myc is assumed to be controlled by a number of positive and negative cis-acting control elements located upstream or within exon 1 and intron 1. However, these regulatory elements are not sufficient for c-myc expression after stable transfection or in transgenic mice. Transcription of c-myc in vivo thus requires additional control elements located outside the tested HindIII-EcoRI gene fragment. In order to identify these putative additional control elements, we mapped DNase I hypersensitive sites around the human c-myc gene in nine different tumor cell lines and in primary lymphocytes. Within the coding and 5' region of the gene, an almost identical pattern of DNase I hypersensitive sites was detected in the various cells. In contrast, chromatin analysis of the c-myc 3' region revealed a complex pattern of constitutive and tissue-specific DNase I hypersensitive sites. In enhancer trap experiments we identified two cis-acting control elements, both co-localizing with DNase I hypersensitive sites, that stimulated c-myc transcription after transient transfection in Raji or HeLa cells. Both regulatory elements exerted their enhancer activity in either orientation and regardless of their location within the plasmids. Both elements also conferred activation on a heterologous promoter. The association of these enhancers with DNase I hypersensitive sites, indicating their functional activity in vivo, make them potential candidates for the postulated regulatory control element(s) required for c-myc expression in vivo.

Rat parietal cell receptors for GLP-1-(7-36) amide: northern blot, cross-linking, and radioligand binding

The intestinal peptide hormone glucagon-like peptide-1 (GLP-1) (7-36) amide is a potent stimulus of H+ production in isolated rat parietal cells, suggesting the presence of specific GLP-1-receptors on this cell type. Our aim was to characterize these receptors. Enzymatically isolated rat gastric mucosal cells (F0) were fractionated by counterflow elutriation, resulting in five fractions (F1-F5) according to increasing cell diameter and parietal cell content (3, 5, 4, 27, 81%). Additional density gradient centrifugation of F4 yielded enriched chief cells (74%; parietal cells: 1%; F6), whereas density gradient centrifugation of F5 almost purified parietal cells (97%; chief cells: 1%; F7). Northern blot of total cellular RNA from F0-F7 with a probe specific for the GLP-1-(7-36) amide receptor revealed two RNA species of 2.7 and 3.6 kb. These messages were present to some extent in small cells (F1, F2), much more pronounced in F5, abundant in F7, barely detectable in F3 and F4, and absent from F6. Cross-linking of 125I-labeled GLP-1-(7-36) amide to parietal cell membranes revealed a single 59-kDa band that was abolished by unlabeled GLP-1-(7-36) amide. Throughout fractions F1-F7 specific binding of 125I-GLP-1-(7-36) amide was correlated with parietal cell content (r = 0.99; P < 0.01) and H+ production ([14C]aminopyrine accumulation) in response to GLP-1-(7-36) amide or histamine (r = 0.96; P < 0.01). Binding was maximal in purified parietal cells (F7), whereas almost no binding was detectable in enriched chief cells (F6). In F7, Scatchard analysis revealed a single class of high-affinity binding sites (KD = 2.8 +/- 0.6 x 10(-10) M, Bmax = 6.8 +/- 1.4 fmol/10(6) cells, 4,096 +/- 793 receptors/parietal cells). The following half-maximal inhibition values were found for GLP-1-(7-36) amide and (1-37) and (1-36) amide: 6.6 +/- 0.9 x 10(-10), 1.4 +/- 0.7 x 10(-7), and 2.6 +/- 0.4 x 10(-7) M, respectively. Pancreatic glucagon, GLP-2, and oxyntomodulin, products of the proglucagon gene, were 3-4 log units less potent displacers while gastric inhibitory peptide, vasoactive intestinal peptide, and secretin were ineffective. We conclude that rat parietal cells are equipped with specific high-affinity receptors for GLP-1-(7-36) amide, which, in addition, are present in as yet unidentified small cells (F1, F2) but not in chief cells.

Regulatory elements in the immunoglobulin kappa locus induce c-myc activation and the promoter shift in Burkitt's lymphoma cells

In Burkitt's lymphoma cells the proto-oncogene c-myc is constantly juxtaposed through chromosomal translocation to one of the immunoglobulin loci on chromosomes 14, 2 or 22. In the majority of cases the chromosomal breakpoint is localized 3' or 5' of the gene leaving the physiological c-myc transcription unit intact. As a consequence of the translocation the c-myc gene on the translocation chromosome becomes transcriptionally activated in such a manner that the c-myc promoter P1 is more active than promoter P2. In order to define elements involved in c-myc activation through t(2;8) translocation we have studied the expression of constructs consisting of c-myc and different parts of the immunoglobulin kappa locus after stable transfection into Burkitt's lymphoma cells. The c-myc gene under the control of the complete Ig kappa locus containing matrix attachment region, intron enhancer, constant kappa gene and 3' enhancer was strongly activated with predominant usage of promoter P1. Deletion analysis revealed that the intron or 3' enhancers alone activated c-myc to a much lesser extent and with normal promoter usage (P1 < P2). The cooperation of the same regulatory elements is required not only for transcriptional activation and induction of the promoter shift but also for down-regulation of promoter P1 of the translocated c-myc allele by sodium butyrate, another characteristic feature of Burkitt's lymphoma cells. This supports the notion that all elements involved in transcriptional activation and dysregulation of c-myc are contained within the myc-Ig specific minichromosome.

Validation of two test systems for detecting tumor promoters and EBV inducers: comparative responses of several agents in DR-CAT Raji cells and in human granulocytes

The response to a number of agents has been compared in two short-term assays used for the detection of virus inducers and tumor promoters: (i) induction of the EBV-DR-promoter in Raji cells, as measured by DR-CAT induction (DR-CAT test) and (ii) induction of the oxidative burst in human PMN, as measured by chemiluminescence in the presence of luminol or lucigenin (CL test). In order to validate the two assays, we have investigated the responses to 12-O-tetradecanoyl-phorbol-13-acetate (TPA), 1,2-dioctanoylglycerol (DAG), phospholipase C (PLC EC-3-1-4-30) and ionophore A23187, which are active in both systems: arachidonic acid, linoleic acid and NaCl were found active only in the CL test. Staurosporine (protein kinase inhibitor), tamoxifen (estrogen antagonist and protein kinase C inhibitor), forskolin (protein kinase A activator), R59949 (diacylglycerol kinase inhibitor), curcumin and N-acetyl-L-cysteine (scavengers of reactive oxygen species) and NaCl acted as inhibitors. A good concordance of the EC50 values of inducing substances was found between the two assays, except for A23187 and DAG, which were required at much higher concentrations in the DR-CAT test. The inhibition patterns by the panel of inhibitors revealed similarities and discrepancies in the induction pathways between the two systems, providing information on their mode of action. The two assays, which complement each other, were shown to detect a number of known or suspected EBV inducers or tumor promoters, and thus appear useful for screening of new compounds or mixtures as well as of potential antiviral and antipromoting substances.

Absence of a paused transcription complex from the c-myc P2 promoter of the translocation chromosome in Burkitt's lymphoma cells: implication for the c-myc P1/P2 promoter shift

We have shown recently that pausing of RNA polymerase II (pol II) at the transcription start site regulates expression from the P2 promoter of the proto-oncogene c-myc. RNAs initiated at the P2 promoter usually contribute > 80% to steady-state c-myc RNA levels in normal cells. In Burkitt's lymphoma (BL) cells c-myc is chromosomally translocated to an immunoglobulin (Ig) gene and preferentially transcribed from the upstream P1 promoter. We have studied the activity of c-myc promoters in two BL cell lines with high expression of P1 RNA. Kinetic nuclear run-on experiments show that the initiation rate at the c-myc P1 promoter in BL2 and BL60 cells is not increased compared with control BJAB cells, whereas the number of paused polymerases at the P2 promoter is greatly diminished. The translocation c-myc gene of BL60 cells was cloned and stably transfected into the BL cell line Raji. The transfected c-myc gene regained the ability to form a paused transcription complex at the c-myc P2 promoter. The data suggest that a paused polymerase at the c-myc P2 promoter impedes transcription from the upstream P1 promoter on a normal c-myc gene. The c-myc gene on the translocation chromosome in BL cells has lost the ability to retain pol II at the P2 promoter, probably by interaction with elements of the adjacent Ig gene locus.

Two antisense promoters in the immunoglobulin mu-switch region drive expression of c-myc in the Burkitt's lymphoma cell line BL67

In the Burkitt's lymphoma (BL) cell line BL67 the first exon of the c-myc gene is fused to the mu-switch region of the immunoglobulin heavy-chain gene (IgH). BL67 cells express IgH/c-myc hybrid RNAs which are initiated in the immunoglobulin locus, transcribed across the chromosomal breakpoint into the first exon of c-myc and spliced using the physiological splice donor and acceptor sites of the c-myc gene. We have isolated cDNAs of these hybrid RNAs and characterized the start points in the Ig heavy-chain gene. Two promoters were identified in the mu-switch region of BL67 cells which give rise to antisense transcription of the mu-gene. These promoters are also active in other BL cell lines, in B cells without Ig translocation and in a T-cell line. Both promoters co-localize with DNAase I-hypersensitive sites, HNF and HSW, in the mu-switch region. The structures of IgH/c-myc hybrid RNAs and of the corresponding promoters are described.

Short-term assays for detection of conditional cancerogens. I. Construction of DR-CAT Raji cells and some of their characteristics as tester cells

A number of agents including the tumor promoter 12-0-tetradecanoyl-phorbol-13-acetate (TPA) (TPA) can induce an abortive virus cycle in the EBV-non-producer Burkitt's-lymphoma line Raji. Two distant regions, DL and DR, of the EBV genome with almost complete homology carry strong promoters which are induced in an abortive or lytic cycle and additionally function as lytic origins of viral DNA replication. To set up a system in which the activity of EBV-inducing agents can be measured in a quantitative and reproducible fashion, we generated a cell line which carries multiple copies of a DR-promoter chloramphenicol-acetyltransferase (CAT) construct on an episomal vector. CAT activity is low in untreated cells, but high upon treatment of the cells with various EBV-inducing agents. Combinations of different agents can produce an over-additive effect. The Raji-DR-CAT cell line may provide a simple quantitative and reproducible test system for EBV-inducing agents, especially for tumor promoters which activate protein kinases C.

The intron enhancer of the immunoglobulin kappa gene activates c-myc but does not induce the Burkitt-specific promoter shift

In Burkitt's lymphoma cells the c-myc gene locus is consistently fused to the constant region of one of the immunoglobulin genes by chromosomal translocation. The translocated c-myc gene is transcriptionally activated and preferentially transcribed from the P1 promoter whenever the exon-intron structure of c-myc remains intact. In order to define elements involved in this promoter shift we have cloned the translocated c-myc allele from Burkitt's lymphoma cell line BL60, which is characterized by several point mutations. The mutated c-myc allele of BL60 was stably introduced into baby hamster kidney and Burkitt's lymphoma cells. S1 nuclease and RNAase protection mapping experiments demonstrated that the mutated c-myc allele was expressed at a low level and with a normal promoter usage (P2 greater than P1) in Burkitt's lymphoma and baby hamster kidney cells. Furthermore, we have studied the expression of a construct consisting of the mutated c-myc allele, part of the bvr1 (Burkitt's variant rearranging region 1) locus, the human immunoglobulin kappa constant region, and the kappa intron enhancer after stable transfection into Burkitt's lymphoma cells. Although c-myc expression was about fivefold increased, the transcripts still initiated predominantly at promoter P2. This indicates that 5 kb of the constant kappa light-chain locus including the kappa intron enhancer is not sufficient to induce the Burkitt's lymphoma-specific promoter shift.

Transcriptional activity across the Epstein-Barr virus genome in Raji cells during latency and after induction of an abortive lytic cycle

We have studied the relative rate of transcription across the Epstein-Barr virus genome in the Burkitt's lymphoma cell line Raji by nuclear run-on analysis during latency and after induction of an abortive lytic cycle with 12-0-tetradecanoylphorbol 13-acetate (TPA) and 5-iodo-2'-deoxyuridine (IUdR). During latency the entire, or almost the entire, viral genome was found to be transcriptionally active to a low or intermediate extent, with some variation in activity along the genome. The fragment with the highest transcriptional activity was EcoRI J, which contains the genes encoding the small nuclear RNAs EBER1 and -2, transcribed predominantly by RNA polymerase III. An intermediate level of transcription was observed between positions 10 and 138 (kb), with areas of slightly higher activity on the large internal repeats and the left duplicated region (DL). The remaining part of the viral genome, between position 138 and the termini, and the termini and position 10 (kb) (with the exception of the EcoRI J fragment), showed very little transcriptional activity, except for the intermediately active regions carrying the righthand oriLyt (DR) and the terminal repeats. Upon induction of the viral genome with TPA and IUdR, the viral genome was transcriptionally active at a rate at least tenfold that seen during latency. Polymerases were not equally distributed along the genome after induction; the highest density was found in regions 48 to 58 kb, 82 to 84 kb, 102 to 104 kb, 118 to 122 kb and 142 to 145 kb of the viral genome. High transcriptional activity correlated with distinct transcription units in some cases, i.e. BamHI H1LF1 (DL), BamHI MLF1, BamHI ZLF1/BamHI RLF1 and BamHI X (thymidine kinase), but not in others (BamHI H2). Besides initiation of transcription, other regulatory processes such as stabilization and processing of primary transcripts may also contribute to regulation of virus gene expression. Addition of cycloheximide completely abolished the transcriptional activation of the genome mediated by TPA and IUdR.

Expression of P0- and P3-RNA from the normal and translocated c-myc allele in Burkitt's lymphoma cells

We have studied the allele specific expression of c-myc P0- and P3-RNA in Burkitt's lymphoma (BL) cells. The steady state levels of P0-RNA show considerable variations in BL cells. Expression of P0-RNA was found to be restricted to the translocated allele, but could be induced by TPA from the normal allele. P0-transcription was particularly sensitive to inhibitors of protein synthesis compared to expression of P1-, P2- and P3-RNA. Transcription of P3-RNA is initiated in the first intron of the c-myc gene and has previously been described to be specific for translocated c-myc alleles in BL cells broken within exon 1 or intron 1. Here we show that P3-RNA is also expressed from an unrearranged c-myc gene. In the BL cell line Raji, substantial amounts of c-myc RNA are derived from the P3-promoter of the normal allele. This indicates that repression of the normal allele in BL cells does not include the P3-promoter. The potential coding capacity of P3-RNA is discussed.

The block of elongation in c-myc exon 1 is abolished in Burkitt's lymphoma cell lines with variant translocation

Dimethylsulfoxide (DMSO) induces a block of c-myc RNA elongation in the human B cell line BJAB. In Burkitt's lymphoma cell lines with variant translocations, which are characterized by mutations in and around the first c-myc exon, DMSO is not capable of inducing the RNA elongation block. The action of DMSO is, however, not restricted to regulation at the level of RNA elongation. In the cell line BL2 with a t(8;22) translocation c-myc steady-state RNA decreased about 20 fold 1 and 2 h after DMSO treatment, followed by an increase to approximately initial levels after 4 h. During the time course of the experiment the usage of the dual promoter P1/P2 shifted from the ratio 3:1 in untreated cells to the ratio of 1:5 in BL2 cells treated with DMSO for 4 h. This promoter shift is presumably regulated at the transcriptional level. In BJAB cells an isolated intragenic transcription was detected at the boundary of intron 1 and exon 2. This transcription appeared 2 to 4 h after addition of DMSO when expression of the c-myc gene was downregulated by blocking RNA elongation at the end of exon 1.

TPA-inducible Epstein-Barr virus genes in Raji cells and their regulation

A number of agents including the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) can induce an abortive virus cycle in the EBV nonproducer Burkitt's lymphoma line Raji. We describe the pattern of viral RNAs transcribed in uninduced cells and in cells treated with TPA for 8 hr, as analyzed by Northern blotting. By comparing the patterns of RNAs observed in cells treated with TPA, TPA plus cycloheximide, or cycloheximide alone, we have tested whether any EBV gene in TPA-treated Raji cells would be inducible directly by TPA in the presence of protein synthesis inhibitors, similarly to immediate-early genes induced by superinfection of Raji cells with P3HR-1 virus in the presence of cycloheximide. We demonstrate here that induction of all early EBV genes is dependent on ongoing protein synthesis. The experiments do not provide an answer to whether TPA acts by activating an initial step in the cascade of virus production or whether TPA has a simultaneous pleiotropic effect on the regulation of a large number of viral genes.

Truncation does not abrogate transcriptional downregulation of the c-myc gene by sodium butyrate in Burkitt's lymphoma cells

We have examined the effect of sodium butyrate, a potent inducer of differentiation in various cell systems, on the steady state RNA level and transcriptional activity of the c-myc gene in Burkitt's lymphoma cells. Following sodium butyrate treatment a rapid decrease of c-myc RNA was observed in all Burkitt's lymphoma cell lines studied, irrespective of the type of translocation, the location of the breakpoint relative to c-myc or of the association with EBV. Since cellular genes induced by interferon are suspected to play a role in c-myc regulation we have studied transcription of the 2-5A synthetase gene in sodium butyrate-treated Burkitt's lymphoma cells. Transcriptional activity and steady state mRNA levels of the 2-5A synthetase gene were induced by sodium butyrate. The time course of induction excluded, however, that the decrease of c-myc RNA is caused by induction of the 2-5A synthetase/RNase L endonuclease system. The reduction of c-myc RNA is caused, at least in part, by a reduced transcription rate, as shown by nuclear run-on analysis. The fact that sodium butyrate is capable of downregulating a truncated c-myc gene indicates that an important target site of transcriptional regulation is located outside the region encompassing the upstream regulatory sequences, the dual promoters and the leader region.

Electron microscopy of binding of Epstein-Barr virus (EBV) nuclear antigen (EBNA-1) to EBV DNA

Specific binding sites for Epstein-Barr virus (EBV) nuclear antigen (EBNA-1), isolated and semipurified from EBV-transformed nonproductive Raji cells, were visualized on the molecule of EBV DNA by electron microscopy and mapped. Two measures had to be applied to counteract the limited purity of the EBNA-1 preparation: (i) EBV DNA/EBNA-1 complexes were specifically enlarged by binding with anti-EBNA-1 (IR-3) IgG antibody. (ii) DNA-binding proteins that did not react with the anti-EBNA-1 antibody were eluted from EBV DNA with 1.5 M NaCl, taking advantage of the resistance of DNA/EBNA-1/anti-EBNA-1 antibody complexes to the high-salt treatment. EBNA-1 bound at the highest relative frequency (greater than 30%) to the EBV DNA map positions of 8.8 +/- 0.3, 10.3 +/- 0.5, and 46.6 +/- 1.2 kb. It bound with a lower but still statistically significant frequency (16%) to the map positions of 64.5 +/- 1.0, 89.7 +/- 1.6, 129.6 +/- 1.1 kb.

[Chromosome translocations and Epstein-Barr virus in Burkitt's lymphoma]

Burkitt's lymphoma is characterized by particular epidemiological features. It is a frequent childhood tumor in children in tropical Africa and occurs at a much lesser frequency all over the world. Chromosomal translocation affecting the long arm of chromosome 8 (band 8q24) and one of the chromosomes carrying the immunoglobulin loci (chromosomes 2, 14 or 22) are regularly observed in Burkitt's lymphoma, regardless of whether the tumor occurred in high or low incidence areas. The prevalence of Burkitt's lymphoma in Africa appears to be related to two factors: holo- or hyperendemic malaria and presence of Epstein-Barr virus genomes in the tumor cells. We present a model of pathogenesis, in which stimulation of B cells by malaria is the primary event in the development of the disease. The risk of the chromosomal translocation should be increased by increasing the number of new B cells generated per time. According to our model, the translocation leads to constitutive c-myc activation and makes the cells responsive to growth factors without inducing proliferation on its own. Infection of a translocation-carrying cell with EBV may provide an additional growth advantage and drive the cell further towards a fully malignant state.

Nucleic acid hybridization for detection of herpes viruses in clinical specimens

A diagnostic hybridization assay for detecting varicella zoster virus (VZV), herpes simplex virus (HSV), and Epstein-Barr virus (EBV) in different clinical specimens was developed using cloned viral DNAs as probes. All probes detected at least 5 pg of homologous DNA and did not cross-react with other viral or cellular DNA. Results of cell culture, serology, and DNA assay were highly concordant. Using a simple standardized protocol for preparation of specimens, hybridization, and washing procedures, this sensitive and specific assay appears to be useful for screening clinical specimens and may be helpful in confirming the serological diagnosis of HSV encephalitis and persistent EBV infections or EBV-associated diseases.

Expression of a nuclear and a cytoplasmic Epstein-Barr virus early antigen after DNA transfer: cooperation of two distant parts of the genome for expression of the cytoplasmic antigen

Expression of Epstein-Barr virus (EBV) antigens was studied after transfection of cloned EBV DNA fragments into baby hamster kidney (BHK) cells. A set of seven widely overlapping clones covering the whole genome of the non-defective Epstein-Barr virus strain M-ABA was used for transfection. Transfer of the cosmid clones into BHK cells resulted in expression of two distinct antigens, as revealed by indirect immunofluorescence using human anti-EBV sera. Staining with human sera of different reactivity against EBV-associated antigens revealed that both types of antigens were related to the early antigen complex. The first type of antigen was detected only in the nuclei of BHK cells that had received DNA of a clone containing HindIII-G, -H, -E, -I2, -O, -I1, and -P. The second type of antigen was found in the cytoplasm of cells cotransfected with clones containing Sal-A and HindIII-I2, -O, -I1, -P, and -C, whereas transfection of both individual clones failed to induce the antigen. Further analysis with subclones identified HindIII-G (5 kilobases) and HindIII-I2 (3 kilobases) plus the rightmost 3 kilobases of Sal-A as the sequences responsible for expression of the nuclear and the cytoplasmic antigen, respectively. The fact that two distant regions of the viral genome are required for expression of a viral antigen provides evidence for intergenomic regulation that can be studied in vitro.

A complete set of overlapping cosmid clones of M-ABA virus derived from nasopharyngeal carcinoma and its similarity to other Epstein-Barr virus isolates

DNA of the transforming, nondefective Epstein-Barr virus (EBV) strain M-ABA, which is derived from nasopharyngeal carcinoma cells, was cloned as large overlapping pieces into the cosmid pHC79 . The termini were cloned from closed circular virus DNA molecules out of M-ABA cell DNA in phage lambda L47 . The large overlapping clones were used to prepare a library of subclones with inserts of 1-15 kb. A detailed restriction enzyme map of M-ABA virus DNA reveals the close similarity to isolates from other sources. The high number of tandem repeats in EBV DNA stresses the importance of using cloning vectors that can be propagated in recA- Escherichia coli hosts.