Showing papers by "University of Zurich published in 1988"
1,175 citations
TL;DR: The data presented demonstrate the existence of membrane proteins with potent nonpermissive substrate properties and suggest that these proteins might play a crucial inhibitory role during development and regeneration in CNS white matter.
Abstract: Lack of neurite growth in optic nerve explants in vitro has been suggested to be due to nonpermissive substrate properties of higher vertebrate central nervous system (CNS) white matter. We have searched for surface components in CNS white matter, which would prevent neurite growth. CNS, but not peripheral nervous system (PNS) myelin fractions from rat and chick were highly nonpermissive substrates in vitro. We have used an in vitro spreading assay with 3T3 cells to quantify substrate qualities of membrane fractions and of isolated membrane proteins reconstituted in artificial lipid vesicles. CNS myelin nonpermissiveness was abolished by treatment with proteases and was not associated with myelin lipid. Nonpermissive proteins were found to be membrane bound and yielded highly nonpermissive substrates upon reconstitution into liposomes. Size fractionation of myelin protein by SDS-PAGE revealed two highly nonpermissive minor protein fractions of Mr 35 and 250-kD. Removal of 35- and of 250-kD protein fractions yielded a CNS myelin protein fraction with permissive substrate properties. Supplementation of permissive membrane protein fractions (PNS, liver) with low amounts of 35- or of 250-kD CNS myelin protein was sufficient to generate highly nonpermissive substrates. Inhibitory 35- and 250-kD proteins were found to be enriched in CNS white matter and were found in optic nerve cell cultures which contained highly nonpermissive, differentiated oligodendrocytes. The data presented demonstrate the existence of membrane proteins with potent nonpermissive substrate properties. Distribution and properties suggest that these proteins might play a crucial inhibitory role during development and regeneration in CNS white matter.
913 citations
TL;DR: T lymphocytes reactive with the product of the Mlsa-allele of the minor lymphocyte stimulating (Mls) locus use a predominant T-cell receptor β-chain variable gene segment (Vβ6), consistent with a model in which tolerance to self antigens is achieved by clonal deletion.
Abstract: T lymphocytes reactive with the product of the Mlsa-allele of the minor lymphocyte stimulating (Mls) locus use a predominant T-cell receptor beta-chain variable gene segment (V beta 6). Such V beta 6-bearing T cells are selectively eliminated in the thymus of Mlsa-bearing mice, consistent with a model in which tolerance to self antigens is achieved by clonal deletion.
884 citations
TL;DR: It is concluded that the nonpermissive substrate properties of CNS white matter are due to these membrane proteins on the surface of differentiated oligodendrocytes and to their in vivo product, myelin.
871 citations
TL;DR: This paper showed that differentiated oligodendrocytes (O4+, A2B5+, GalC+) represented a nonpermissive substrate for neuronal adhesion and neurite growth.
Abstract: To study the interaction of neurons with CNS glial cells, dissociated sympathetic or sensory ganglion cells or fetal retinal cells were plated onto cultures of dissociated optic nerve glial cells of young rats. Whereas astrocytes favored neuron adhesion and neurite outgrowth, oligodendrocytes differed markedly in their properties as neuronal substrates. Immature (O4+, A2B5+, GalC-) oligodendrocytes were frequently contacted by neurons and neurites. In contrast, differentiated oligodendrocytes (O4+, A2B5-, GalC+) represented a nonpermissive substrate for neuronal adhesion and neurite growth. When neuroblastoma cells or 3T3 fibroblasts were plated into optic nerve glial cultures, the same differences were observed; differentiated oligodendrocytes were nonpermissive for cell adhesion, neurite growth, or fibroblast spreading. These nonpermissive oligodendrocytes were characterized by a radial, highly branched process network, often contained myelin basic protein, and may, therefore, correspond to cells actively involved in the production of myelin-like membranes. Isolated myelin from adult rat spinal cord was adsorbed to polylysine-coated culture dishes and tested as a substrate for peripheral neurons, neuroblastoma cells, or 3T3 cells. Again, cell attachment, neurite outgrowth, and fibroblast spreading was strongly impaired. General physicochemical properties of myelin were not responsible for this effect, since myelin from rat sciatic nerves favored neuron adhesion and neurite growth as well as spreading of 3T3 cells. These results show that differentiated oligodendrocytes express nonpermissive substrate properties, which may be of importance in CNS development or regeneration.
684 citations
TL;DR: This work experimentally manipulates ants' outbound trajectories to elucidate the ant's way of computing its mean home vector and shows that the ants solve this path integration problem not by performing a true vector summation but by employing a computationally simple approximation.
Abstract: Foraging desert ants, Cataglyphis fortis, continually keep track of their own posotions relative to home— i.e., integrate their tortuous outbound routes and return home along straight (inbound) routes. By experimentally manipulating the ants' outbound trajectories we show that the ants solve this path integration problem not by performing a true vector summation (as a human navigator does) but by employing a computationally simple approximation. This approximation is characterized by small, but systematic, navigational errors that helped us elucidate the ant's way of computing its mean home vector.
651 citations
TL;DR: Amino acid sequencing of the purified peptide and oligonucleotide-directed cDNA cloning established that the peptide consists of 36 amino acids, and appears to be synthesized as a precursor with a hydrophobic signal sequence of 19 residues at its N-terminal end.
625 citations
TL;DR: Lysates of non–transformed E. coli grown at either temperature rendered initially soluble human recombinant IFN–α2 insoluble at 37° but not at 0° or 30°C, and insolubilization was not abolished by nuclease treatment.
Abstract: Human interferon–α2 (IFN–α2), an 18 kD, acidic protein, human interferon–γ (IFN–γ), a 17 kD, basic protein, and the interferon–induced murine protein Mx (72 kD) were all found in aggregates when produced in genetically engineered strains of E. coli grown at 37°C. However, at a growth temperature of 23–30°C, 30–90% of the recombinant protein was soluble. The temperature effect was not directly dependent on the concentration of the protein and was observed for several E. coli strains and for different plasmid constructions. Lysates of non–transformed E. coli grown at either temperature rendered initially soluble human recombinant IFN–α2 insoluble at 37° but not at 0° or 30°C. Insolubilization was not abolished by nuclease treatment, and may involve sulfhydryl group shuffling, as sulfhydryl reducing agents added to a mock lysate gave a similar temperature dependent precipitation.
468 citations
TL;DR: A cDNA encoding the human interferon-gamma receptor was isolated from a lambda gt11 expression library using a polyclonal antireceptor antiserum and transfected into mouse cells, suggesting the need for species-specific cofactors in receptor function.
449 citations
University of Edinburgh1, Curie Institute2, University of Gothenburg3, University of Oslo4, Netherlands Cancer Institute5, Institut Gustave Roussy6, Université libre de Bruxelles7, University of Glasgow8, University of Zurich9, Russian Academy10, University of Alabama at Birmingham11, Martin Luther University of Halle-Wittenberg12
TL;DR: The absence ofLocal recurrence in the group of patients with a primary melanoma thinner than 1 mm and the very low rate of local recurrences indicate that narrow excision is a safe and effective procedure for such patients.
Abstract: Although wide surgical excision is the accepted treatment for thin malignant melanomas, there is reason to believe that narrower margins may be adequate. We conducted a randomized prospective study to assess the efficacy of narrow excision (excision with 1-cm margins) for primary melanomas no thicker than 2 mm. Narrow excision was performed in 305 patients, and wide excision (margins of 3 cm or more) was performed in 307 patients. The major prognostic criteria were well balanced in the two groups. The mean thickness of melanomas was 0.99 mm in the narrow-excision group and 1.02 mm in the wide-excision group. The subsequent development of metastatic disease involving regional nodes and distant organs was not different in the two groups (4.6 and 2.3 percent, respectively, in the narrow-excision group, as compared with 6.5 and 2.6 percent in the wide-excision group). Disease-free survival rates and overall survival rates (mean follow-up period, 55 months) were also similar in the two groups. Only three patients had a local recurrence as a first relapse. All had undergone narrow excision, and each had a primary melanoma with a thickness of 1 mm or more. The absence of local recurrence in the group of patients with a primary melanoma thinner than 1 mm and the very low rate of local recurrences indicate that narrow excision is a safe and effective procedure for such patients.
445 citations
TL;DR: The results support the somatomedin hypothesis, but they also stress the role of GH as a modulator of IGF-I action, which mimics GH effects in hypophysectomized rats.
Abstract: Recombinant human insulin-like growth factor I (rhIGF-I) was infused subcutaneously into hypophysectomized rats for as long as 18 days. Three hundred micrograms (39 nmol) of rhIGF-I per day and 200 milliunits (4.5 nmol) of human growth hormone (hGH) per day increased body weight, tibial epiphyseal width, longitudinal bone growth, and trabecular bone formation similarly. Weight gains of the kidneys and spleen, however, were greater with rhIGF-I than with hGH, whereas the weight of the epididymal fat pads was reduced with rhIGF-I. The weight of the thymus was increased by rhIGF-I treatment. Thus, IGF-I administered over a prolonged period of time mimics GH effects in hypophysectomized rats. Quantitative differences between rhIGF-I and hGH treatment with respect to organ weights may be related to different forms of circulating IGF-I or may be due to independent effects of GH and IGF-I. The results support the somatomedin hypothesis, but they also stress the role of GH as a modulator of IGF-I action.
TL;DR: Twelve monoclonal antibodies (McAB) produced against carp-II parvalbumin recognize determinants conserved in fish, chicken, mouse, rat, monkey and human parValbumin and are shown to use in the qualitative detection of paravalbumin (PV) by immunohistochemistry, in the quantitation of parvalsbumin by radioimmunoassay and in the detection ofParvalbumIn on immunoblots.
TL;DR: It is proposed that the cluster of mutations in the MIBE case, and other combinations of mutationsIn other cases, favored propagation of MV infections in brain cells by conferring a selective advantage to the mutated genomes.
TL;DR: The complementary DNA coding for a lymphocyte-specific transcription factor binding to the DNA 'octamer' sequence TNATTTGCAT has been cloned and the nucleotide sequence shows homology to the homoeobox domain.
Abstract: The complementary DNA coding for a lymphocyte-specific transcription factor binding to the DNA 'octamer' sequence TNATTTGCAT has been cloned. The nucleotide sequence shows homology to the homoeobox domain. Expression of this cDNA in HeLa cells is sufficient for a strong transcriptional activation of B-cell-specific promoters.
TL;DR: In contrast to the case of hydrogen, which is not known to form a paramagnetic state in semiconductors, two coexisting types of muonium states are seen as discussed by the authors.
Abstract: Positive muons implanted into diamond and zincblende-structured semiconductors often form hydrogen-like paramagnetic muonium (${\ensuremath{\mu}}^{+}\ensuremath{-}{e}^{\ensuremath{-}}$) states whose characteristics can be investigated with the "muon spin rotation" ($\ensuremath{\mu}\mathrm{SR}$) technique. In contrast to the case of hydrogen, which is not known to form a paramagnetic state in semiconductors, two coexisting types of muonium states are seen. "Mu" with a large isotropic hyperfine interaction, and "${\mathrm{Mu}}^{*}$" with a small [111]-axially symmetric hyperfine interaction. Both "spectroscopic" properties of these states, such as the electronic $g$ factors and the nuclear hyperfine interactions, and "dynamic" properties, such as their diffusion rates and their rates of interconversion, are accessible with $\ensuremath{\mu}\mathrm{SR}$. Direct information about the site of the muonium states is available using the channeling effect of the positron from muon decay in a crystalline host. The techniques for probing semiconductors with positive muons are described in this review, and the results they have provided to date are critically discussed. The considerable amount of theoretical work that has been invested in microscopic models of Mu and ${\mathrm{Mu}}^{*}$ is also summarized.
TL;DR: In this paper, the analysis of dynamical systems in terms of spectra of singularities is extended to higher dimensions and to non-hyperbolic systems, and the generalized partial dimensions of the invariant measure and the distribution of effective Liapunov exponents for hyperbolic attractors are investigated.
Abstract: The analysis of dynamical systems in terms of spectra of singularities is extended to higher dimensions and to nonhyperbolic systems Prominent roles in our approach are played by the generalized partial dimensions of the invariant measure and by the distribution of effective Liapunov exponents For hyperbolic attractors, the latter determines the metric entropies and provides one constraint on the partial dimensions For nonhyperbolic attractors, there are important modifications We discuss them for the examples of the logistic and Henon map We show, in particular, that the generalized dimensions have singularities with noncontinuous derivative, similar to first-order phase transitions in statistical mechanics
TL;DR: The primary structure of human P1 is determined, its functional properties are re-examine, and the question of homologous restriction factor is addressed.
Abstract: Perforin (P1) is a cytolytic protein with similarity to complement component C9. P1 has been described as a unique component of murine cytolytic T-cell and rat natural killer cell granules Previous studies indicated that human granules and P1 differed from murine granules and P1 in that they appeared to be cytolytically less active and lacked the haemolytic activity characteristic of P1. It has been suggested that P1, like C9, is under the control of the homologous restriction factor. Here we determine the primary structure of human P1, re-examine its functional properties, and address the question of homologous restriction.
TL;DR: It is argued that in computer-assisted generalization, the spatial modelling process can be simulated only by strategies based on understanding and not by a mere sequence of operational processing steps.
Abstract: This paper reviews the prospects of computer-assisted generalization of spatial data. Generalization as a general human activity is first considered in a broad context and map generalization is defined as a special variant of spatial modelling. It is then argued that in computer-assisted generalization, the spatial modelling process can be simulated only by strategies based on understanding and not by a mere sequence of operational processing steps. A conceptual framework for knowledge-based generalization is then presented which can be broken down into five steps: structure recognition, process recognition, process modelling, process execution and display. With reference to the goals of map generalization we identified tasks of statistical and cartographic generalization. The use of these types of tasks is discussed in relation to the concepts of digital landscape models (DLM) and digital cartographic models (DCM). A literature review is then presented in the context of this conceptual framework...
TL;DR: The studies show that neither binding in vitro, nor transcription in vivo and in vitro are affected by methylation of the Sp1 binding site, and the possibility that binding of Sp1 factor, which is often associated with promoters of housekeeping genes, prevents CpG methylation is discussed.
Abstract: In vertebrates, a negative correlation between gene activity and CpG methylation of DNA, notably in the promoter region, is well established. Therefore, it is conceivable that differential binding of transcription factors to methylated versus unmethylated binding sites is crucial for gene activity. Since the consensus binding site of transcription factor Sp1 contains a central CpG, we have investigated the binding of Sp1 factor to unmethylated and synthetically CpG-methylated DNA. A strong Sp1 binding site was methylated on both strands at two CpG positions, located in the center and at the periphery of the recognition sequence. Our studies show that neither binding in vitro, nor transcription in vivo and in vitro are affected by methylation of the Sp1 binding site. We discuss the possibility that binding of Sp1 factor, which is often associated with promoters of housekeeping genes, prevents CpG methylation.
TL;DR: If there is one thing the financial world is not short of it’s financial technology start-ups, incubators, ‘sandboxes’ and innovation centres, the intense interest in financial technology startups and innovation is a natural evolution of technology in the financialworld.
Abstract: If there is one thing the financial world is not short of it’s financial technology start-ups, incubators, ‘sandboxes’ and innovation centres. The intense interest in financial technology startups and innovation is a natural evolution of technology in the financial world. First institutions built their own infrastructures, applications and services, then they bought them from vendors and many eventually outsourced some technologies and operations to third parties.
TL;DR: PEDV-infected cells showed a distinct cytoplasmic fluorescence when examined by a fluorescent-antibody-staining technique and had typical coronavirus morphology when viewed by electron microscopy.
Abstract: Porcine epidemic diarrhea virus (PEDV) was adapted to serial propagation in Vero cell cultures by adding trypsin to the medium. PEDV-infected cells showed a distinct cytoplasmic fluorescence when examined by a fluorescent-antibody-staining technique. Cytopathic effects, such as vacuolation, formation of syncytia, and fusion of cells, were detected even at passage 1 of the PEDV in Vero cells. Once adapted, the virus induced numerous syncytia containing over 100 nuclei. From virus passage 5 on, all cells forming the monolayer were fused and totally destroyed within 24 h after inoculation. Cell culture-grown PEDV had typical coronavirus morphology when viewed by electron microscopy. Attempts to propagate PEDV in several primary and secondary fetal porcine cell cultures in the presence or absence of trypsin were unsuccessful. Images
TL;DR: An MRE of the mouse metallothionein‐I gene (MREd) is analysed and it is demonstrated that this can function over long distances as a bona fide metal ion‐inducible enhancer.
Abstract: Heavy metal ions are effective inducers of metallothionein gene transcription. The metal response is dependent on short DNA motifs, so-called MREs (metal responsive elements) that occur in multiple copies in the promoter region of these genes. We have analysed an MRE of the mouse metallothionein-I gene (MREd) and we demonstrate that this can function over long distances as a bona fide metal ion-inducible enhancer. The transcription factor Sp1 and a zinc-inducible factor, designated MTF-1, bind to the MREd enhancer in vitro. The combined use of MREd mutants in a transient assay in HeLa cells and a competition band shift assay show that the zinc-inducible formation of the MTF-1/DNA complex in vitro correlates with zinc-inducible transcription in vivo. A chemical methylation interference assay revealed remarkably similar but non-identical guanine interference patterns for the MTF-1 and Sp1 complexes, which may mean that MTF-1 is related to the Sp1 factor.
TL;DR: This chapter discusses the prenatal adverse effects of nicotine on the developing brain with actions of nutrition, metabolism and endocrine systems of both fetal and maternal organisms, including the placenta.
Abstract: Publisher Summary This chapter discusses the prenatal adverse effects of nicotine on the developing brain. Nicotine acts on many different central and peripheral processes in the adult organism. Its developmental effects can be expected to result from an interaction of direct effects on the developing brain with actions of nutrition, metabolism and endocrine systems of both fetal and maternal organisms, including the placenta. Nicotine affects the materno-fetal unit through multiple actions. Specific direct actions of nicotine on the developing brain seem possible during a major part of prenatal life, because binding sites for [ 3 H] nicotine are already detectable in the central nervous system of the rat at late embryonic stages. Actions of nicotine at central cholinergic receptor sites combine in a complex way with effects of the drug on circulation, metabolism and endocrine systems of mother and fetus. Children of mothers who smoked during pregnancy display symptoms of minimal brain dysfunction or attention deficit disorder (ADD). Analogous behavioral abnormalities are found in prenatally nicotine-exposed animals.
TL;DR: The successful demonstration of functional synaptic connections between co-cultured slices suggests that this technique offers a unique approach for studying synaptic transmission between remote brain areas.
TL;DR: The results suggest that PV-containing neurons include basket and axo-axonic cells, a particular subpopulation of GABAergic neurons, in the hippocampus studied by immunocytochemistry.
Abstract: The structural features of PV-immunoreactive (PV-I) neurons, a particular subpopulation of GABAergic neurons, in the hippocampus were studied by immunocytochemistry. The PV-I cell bodies were concentrated within the stratum pyramidale (SP) and stratum oriens (SO) in the hippocampus. PV-I puncta were frequent in SP, while they were rarely seen in other layers. The dendritic arborization of PV-I neurons resembled that of some of the nonpyramidal cells observed after Golgi-impregnation. The most commonly observed PV-I neurons had their perikarya located in SP with dendrites extending into SO and the stratum radiatum (SR). Most of the dendrites in SR had typical beaded or varicose segments. The dendrites extending into SO had few beaded parts. There were many bipolar and multipolar neurons with smooth dendrites in SO, but only a small number of such multipolar neurons in SR. An electron microscopic analysis revealed that PV-I products were located to perikarya, dendrites, myelinated axons and synaptic boutons. The perikarya of PV-I neurons exhibited several ultrastructural features of nonpyramidal cells, e.g., abundant cisternae of endoplasmic reticulum, mitochondria and other perikaryal organelles, an infolded nuclear envelope and intranuclear inclusions. They received many asymmetric synapses with round presynaptic vesicles. There were numerous PV-I boutons, presumably axonal endings, covering the pyramidal cell bodies. The PV-I boutons also contacted the axon initial segments and proximal dendrites of the pyramidal cells. In addition PV-I terminals were found on somata and dendrites of both PV-I or PV-negative nonpyramidal cells. The results suggest that PV-containing neurons include basket and axo-axonic cells.
TL;DR: The results found for the two model infections were paralleled by findings in humans; CSF from three out of three patients with bacterial meningitis examined during the first day of hospitalization showed significant levels of TNF-alpha; none of the CSF obtained later than 3 d after hospitalization was positive.
Abstract: To evaluate the potential role of cachectin/TNF-alpha in the pathogenesis of bacterial and viral meningitis, concentrations and kinetics of TNF-alpha were determined in cerebrospinal fluid (CSF). After intracerebral, but not systemic, infection with Listeria monocytogenes in mice, TNF-alpha was detected as early as 3 h after infection reaching maximum titers after 24 h. However, TNF-alpha was not found in serum during the course of Listeria infection. In contrast to bacterial meningitis, no TNF-alpha was detected at any time in CSF of mice suffering from severe lymphocytic choriomeningitis induced by intracerebral infection with lymphocytic choriomeningitis virus. This difference is striking since both model infections led to a massive infiltration of polymorphonuclear and mononuclear leukocytes into the meninges and CSF. The results found for the two model infections were paralleled by findings in humans; CSF from three out of three patients with bacterial meningitis examined during the first day of hospitalization showed significant levels of TNF-alpha; none of the CSF obtained later than 3 d after hospitalization was positive. In addition, similarly to what was found in mice with viral meningitis, zero out of seven patients with viral meningitis had detectable TNF-alpha in CSF.
TL;DR: The gene transformer-2 (tra-2) of Drosophila is necessary not only for female sexual differentiation but also for normal spermatogenesis in males, and its putative protein has a domain that is homologous to RNA binding proteins, suggesting that the tra-2 protein might achieve the female-specific splicing of the transcript of dsx, a sex-determining gene whose mode of expression depends on Tra-2.
TL;DR: In this review the current state of the understanding of endocrine tumors of the pancreas is considered, based on the experience with a series of 365 tumors, and special emphasis is put on the immunocytochemical profile and the biological features of the respective tumors.
Abstract: In this review the current state of our understanding of endocrine tumors of the pancreas is considered. It is based on the experience with a series of 365 tumors. The first part of the article focuses on origin and classification, markers, frequency, criteria of malignancy as well as general structural features of the pancreatic endocrine tumors. In the second half of the article the functioning tumors, i.e. tumors that cause hormonal syndromes, and the nonfunctioning tumors as well as the endocrine tumors associated with multiple endocrine neoplasia type 1 are dealt with in detail. Special emphasis is put on the immunocytochemical profile and the biological features of the respective tumors.
TL;DR: It is suggested that activated mature T cells are required for development of disease and production of both BSF-2 and IFN-gamma, which may be instrumental in local production of antiviral antibodies by B lymphocytes/plasma cells invading the CNS during viral CNS disease.
Abstract: Synthesis of B cell-stimulating factor-2 (BSF-2) and IFN-gamma was shown in cerebrospinal fluids (CSF) collected from mice with experimental viral meningitis. In the CSF, the level of BSF-2 started to increase 24 h after intracerebral infection with lymphocytic choriomeningitis virus (LCMV) with rapid increase after day 4. IFN-gamma was not detected in the CSF before day 5 or 6 after infection, but increased sharply thereafter. In athymic nude mice, LCMV infection did not result in meningitis, and both BSF-2 and IFN-gamma levels were only slightly and transiently elevated. These findings suggest that activated mature T cells are required for development of disease and production of both BSF-2 and IFN-gamma. As observed in mice, BSF-2 was also detected in 16 out of 19 CSF samples collected from patients with acute viral infections of the central nervous system (CNS). Intrathecal production of BSF-2 and IFN-gamma may be instrumental in local production of antiviral antibodies by B lymphocytes/plasma cells invading the CNS during viral CNS disease.
TL;DR: A role of the novel octamer factor in the long range activation by the IgH enhancer is proposed and the proteolytic clipping bandshift assay (PCBA) technique is used to distinguish the three different forms found in B cells.
Abstract: The octamer sequence ATGCAAAT is found in the promoters of immunoglobulin (Ig) heavy and light chain genes and in the heavy chain enhancer and is a major determinant of the cell type specific expression of Ig genes in B cells. An apparent paradox is that the same sequence serves as an upstream promoter or enhancer element in a variety of housekeeping genes such as the histone H2B and U snRNA genes. The differential usage of this regulatory sequence motif is thought to be mediated by different species of octamer binding proteins. One species of 100 kd, designated OTF-1, is present in all cell types and may exert its activating function only when it can interact with additional adjacent transcription factors. The lymphoid cell specific octamer binding protein of 60 kd (OTF-2A) specifically stimulates Ig promoters which consist essentially of a TATA-box and an octamer sequence upstream of it. Here we present evidence for yet another B cell specific octamer binding protein of 75 kd (OTF-2B). From several findings, including the absence of OTF-2B (but not OTF-2A) from a lymphocyte line that cannot respond to the IgH enhancer, we propose a role of the novel octamer factor in the long range activation by the IgH enhancer. We have used the proteolytic clipping bandshift assay (PCBA) technique to distinguish the three different forms found in B cells. This analysis indicates that the 75 kd-species OTF-2B is closely related to the 60 kd species OTF-2A.